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 <div class="section" id="module-unittest.mock">
<h1>26.5. <a class="reference internal" href="#module-unittest.mock" title="unittest.mock: Mock object library."><code class="xref py py-mod docutils literal notranslate">unittest.mock</code></a> — mock object library<a class="headerlink" href="#module-unittest.mock" title="Permalink to this headline">¶</a></h1>
<div class="versionadded">
New in version 3.3.
</div>
Source code: <a class="reference external" href="https://github.com/python/cpython/tree/3.6/Lib/unittest/mock.py">Lib/unittest/mock.py</a>
<hr class="docutils" />
<a class="reference internal" href="#module-unittest.mock" title="unittest.mock: Mock object library."><code class="xref py py-mod docutils literal notranslate">unittest.mock</code></a> is a library for testing in Python. It allows you to
replace parts of your system under test with mock objects and make assertions
about how they have been used.
<a class="reference internal" href="#module-unittest.mock" title="unittest.mock: Mock object library."><code class="xref py py-mod docutils literal notranslate">unittest.mock</code></a> provides a core <a class="reference internal" href="#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate">Mock</code></a> class removing the need to
create a host of stubs throughout your test suite. After performing an
action, you can make assertions about which methods / attributes were used
and arguments they were called with. You can also specify return values and
set needed attributes in the normal way.
Additionally, mock provides a <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> decorator that handles patching
module and class level attributes within the scope of a test, along with
<a class="reference internal" href="#unittest.mock.sentinel" title="unittest.mock.sentinel"><code class="xref py py-const docutils literal notranslate">sentinel</code></a> for creating unique objects. See the <a class="reference internal" href="#quick-guide">quick guide</a> for
some examples of how to use <a class="reference internal" href="#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate">Mock</code></a>, <a class="reference internal" href="#unittest.mock.MagicMock" title="unittest.mock.MagicMock"><code class="xref py py-class docutils literal notranslate">MagicMock</code></a> and
<a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a>.
Mock is very easy to use and is designed for use with <a class="reference internal" href="unittest.html#module-unittest" title="unittest: Unit testing framework for Python."><code class="xref py py-mod docutils literal notranslate">unittest</code></a>. Mock
is based on the ‘action -&gt; assertion’ pattern instead of ‘record -&gt; replay’
used by many mocking frameworks.
There is a backport of <a class="reference internal" href="#module-unittest.mock" title="unittest.mock: Mock object library."><code class="xref py py-mod docutils literal notranslate">unittest.mock</code></a> for earlier versions of Python,
available as <a class="reference external" href="https://pypi.org/project/mock">mock on PyPI</a>.
<div class="section" id="quick-guide">
<h2>26.5.1. Quick Guide<a class="headerlink" href="#quick-guide" title="Permalink to this headline">¶</a></h2>
<a class="reference internal" href="#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate">Mock</code></a> and <a class="reference internal" href="#unittest.mock.MagicMock" title="unittest.mock.MagicMock"><code class="xref py py-class docutils literal notranslate">MagicMock</code></a> objects create all attributes and
methods as you access them and store details of how they have been used. You
can configure them, to specify return values or limit what attributes are
available, and then make assertions about how they have been used:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; from unittest.mock import MagicMock
&gt;&gt;&gt; thing = ProductionClass()
&gt;&gt;&gt; thing.method = MagicMock(return_value=3)
&gt;&gt;&gt; thing.method(3, 4, 5, key=&#39;value&#39;)
3
&gt;&gt;&gt; thing.method.assert_called_with(3, 4, 5, key=&#39;value&#39;)
</pre></div>
</div>
<code class="xref py py-attr docutils literal notranslate">side_effect</code> allows you to perform side effects, including raising an
exception when a mock is called:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock(side_effect=KeyError(&#39;foo&#39;))
&gt;&gt;&gt; mock()
Traceback (most recent call last):
 ...
KeyError: &#39;foo&#39;
</pre></div>
</div>
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; values = {&#39;a&#39;: 1, &#39;b&#39;: 2, &#39;c&#39;: 3}
&gt;&gt;&gt; def side_effect(arg):
... return values[arg]
...
&gt;&gt;&gt; mock.side_effect = side_effect
&gt;&gt;&gt; mock(&#39;a&#39;), mock(&#39;b&#39;), mock(&#39;c&#39;)
(1, 2, 3)
&gt;&gt;&gt; mock.side_effect = [5, 4, 3, 2, 1]
&gt;&gt;&gt; mock(), mock(), mock()
(5, 4, 3)
</pre></div>
</div>
Mock has many other ways you can configure it and control its behaviour. For
example the spec argument configures the mock to take its specification
from another object. Attempting to access attributes or methods on the mock
that don’t exist on the spec will fail with an <a class="reference internal" href="exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate">AttributeError</code></a>.
The <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> decorator / context manager makes it easy to mock classes or
objects in a module under test. The object you specify will be replaced with a
mock (or other object) during the test and restored when the test ends:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; from unittest.mock import patch
&gt;&gt;&gt; @patch(&#39;module.ClassName2&#39;)
... @patch(&#39;module.ClassName1&#39;)
... def test(MockClass1, MockClass2):
... module.ClassName1()
... module.ClassName2()
... assert MockClass1 is module.ClassName1
... assert MockClass2 is module.ClassName2
... assert MockClass1.called
... assert MockClass2.called
...
&gt;&gt;&gt; test()
</pre></div>
</div>
<div class="admonition note">
Note
When you nest patch decorators the mocks are passed in to the decorated
function in the same order they applied (the normal python order that
decorators are applied). This means from the bottom up, so in the example
above the mock for <code class="docutils literal notranslate">module.ClassName1</code> is passed in first.
With <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> it matters that you patch objects in the namespace where they
are looked up. This is normally straightforward, but for a quick guide
read <a class="reference internal" href="#where-to-patch">where to patch</a>.
</div>
As well as a decorator <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> can be used as a context manager in a with
statement:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; with patch.object(ProductionClass, &#39;method&#39;, return_value=None) as mock_method:
... thing = ProductionClass()
... thing.method(1, 2, 3)
...
&gt;&gt;&gt; mock_method.assert_called_once_with(1, 2, 3)
</pre></div>
</div>
There is also <a class="reference internal" href="#unittest.mock.patch.dict" title="unittest.mock.patch.dict"><code class="xref py py-func docutils literal notranslate">patch.dict()</code></a> for setting values in a dictionary just
during a scope and restoring the dictionary to its original state when the test
ends:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; foo = {&#39;key&#39;: &#39;value&#39;}
&gt;&gt;&gt; original = foo.copy()
&gt;&gt;&gt; with patch.dict(foo, {&#39;newkey&#39;: &#39;newvalue&#39;}, clear=True):
... assert foo == {&#39;newkey&#39;: &#39;newvalue&#39;}
...
&gt;&gt;&gt; assert foo == original
</pre></div>
</div>
Mock supports the mocking of Python <a class="reference internal" href="#magic-methods">magic methods</a>. The
easiest way of using magic methods is with the <a class="reference internal" href="#unittest.mock.MagicMock" title="unittest.mock.MagicMock"><code class="xref py py-class docutils literal notranslate">MagicMock</code></a> class. It
allows you to do things like:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = MagicMock()
&gt;&gt;&gt; mock.__str__.return_value = &#39;foobarbaz&#39;
&gt;&gt;&gt; str(mock)
&#39;foobarbaz&#39;
&gt;&gt;&gt; mock.__str__.assert_called_with()
</pre></div>
</div>
Mock allows you to assign functions (or other Mock instances) to magic methods
and they will be called appropriately. The <a class="reference internal" href="#unittest.mock.MagicMock" title="unittest.mock.MagicMock"><code class="xref py py-class docutils literal notranslate">MagicMock</code></a> class is just a Mock
variant that has all of the magic methods pre-created for you (well, all the
useful ones anyway).
The following is an example of using magic methods with the ordinary Mock
class:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock()
&gt;&gt;&gt; mock.__str__ = Mock(return_value=&#39;wheeeeee&#39;)
&gt;&gt;&gt; str(mock)
&#39;wheeeeee&#39;
</pre></div>
</div>
For ensuring that the mock objects in your tests have the same api as the
objects they are replacing, you can use <a class="reference internal" href="#auto-speccing">auto-speccing</a>.
Auto-speccing can be done through the autospec argument to patch, or the
<a class="reference internal" href="#unittest.mock.create_autospec" title="unittest.mock.create_autospec"><code class="xref py py-func docutils literal notranslate">create_autospec()</code></a> function. Auto-speccing creates mock objects that
have the same attributes and methods as the objects they are replacing, and
any functions and methods (including constructors) have the same call
signature as the real object.
This ensures that your mocks will fail in the same way as your production
code if they are used incorrectly:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; from unittest.mock import create_autospec
&gt;&gt;&gt; def function(a, b, c):
... pass
...
&gt;&gt;&gt; mock_function = create_autospec(function, return_value=&#39;fishy&#39;)
&gt;&gt;&gt; mock_function(1, 2, 3)
&#39;fishy&#39;
&gt;&gt;&gt; mock_function.assert_called_once_with(1, 2, 3)
&gt;&gt;&gt; mock_function(&#39;wrong arguments&#39;)
Traceback (most recent call last):
 ...
TypeError: &lt;lambda&gt;() takes exactly 3 arguments (1 given)
</pre></div>
</div>
<a class="reference internal" href="#unittest.mock.create_autospec" title="unittest.mock.create_autospec"><code class="xref py py-func docutils literal notranslate">create_autospec()</code></a> can also be used on classes, where it copies the signature of
the <code class="docutils literal notranslate">__init__</code> method, and on callable objects where it copies the signature of
the <code class="docutils literal notranslate">__call__</code> method.
</div>
<div class="section" id="the-mock-class">
<h2>26.5.2. The Mock Class<a class="headerlink" href="#the-mock-class" title="Permalink to this headline">¶</a></h2>
<a class="reference internal" href="#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate">Mock</code></a> is a flexible mock object intended to replace the use of stubs and
test doubles throughout your code. Mocks are callable and create attributes as
new mocks when you access them <a class="footnote-reference" href="#id3" id="id1">[1]</a>. Accessing the same attribute will always
return the same mock. Mocks record how you use them, allowing you to make
assertions about what your code has done to them.
<a class="reference internal" href="#unittest.mock.MagicMock" title="unittest.mock.MagicMock"><code class="xref py py-class docutils literal notranslate">MagicMock</code></a> is a subclass of <a class="reference internal" href="#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate">Mock</code></a> with all the magic methods
pre-created and ready to use. There are also non-callable variants, useful
when you are mocking out objects that aren’t callable:
<a class="reference internal" href="#unittest.mock.NonCallableMock" title="unittest.mock.NonCallableMock"><code class="xref py py-class docutils literal notranslate">NonCallableMock</code></a> and <a class="reference internal" href="#unittest.mock.NonCallableMagicMock" title="unittest.mock.NonCallableMagicMock"><code class="xref py py-class docutils literal notranslate">NonCallableMagicMock</code></a>
The <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> decorators makes it easy to temporarily replace classes
in a particular module with a <a class="reference internal" href="#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate">Mock</code></a> object. By default <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> will create
a <a class="reference internal" href="#unittest.mock.MagicMock" title="unittest.mock.MagicMock"><code class="xref py py-class docutils literal notranslate">MagicMock</code></a> for you. You can specify an alternative class of <a class="reference internal" href="#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate">Mock</code></a> using
the new_callable argument to <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a>.
<dl class="class">
<dt id="unittest.mock.Mock">
class <code class="descclassname">unittest.mock.</code><code class="descname">Mock</code>(spec=None, side_effect=None, return_value=DEFAULT, wraps=None, name=None, spec_set=None, unsafe=False, **kwargs)<a class="headerlink" href="#unittest.mock.Mock" title="Permalink to this definition">¶</a></dt>
<dd>Create a new <a class="reference internal" href="#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate">Mock</code></a> object. <a class="reference internal" href="#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate">Mock</code></a> takes several optional arguments
that specify the behaviour of the Mock object:
<ul>
<li>spec: This can be either a list of strings or an existing object (a
class or instance) that acts as the specification for the mock object. If
you pass in an object then a list of strings is formed by calling dir on
the object (excluding unsupported magic attributes and methods).
Accessing any attribute not in this list will raise an <a class="reference internal" href="exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate">AttributeError</code></a>.
If spec is an object (rather than a list of strings) then
<a class="reference internal" href="stdtypes.html#instance.__class__" title="instance.__class__"><code class="xref py py-attr docutils literal notranslate">__class__</code></a> returns the class of the spec object. This
allows mocks to pass <a class="reference internal" href="functions.html#isinstance" title="isinstance"><code class="xref py py-func docutils literal notranslate">isinstance()</code></a> tests.
</li>
<li>spec_set: A stricter variant of spec. If used, attempting to set
or get an attribute on the mock that isn’t on the object passed as
spec_set will raise an <a class="reference internal" href="exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate">AttributeError</code></a>.
</li>
<li>side_effect: A function to be called whenever the Mock is called. See
the <a class="reference internal" href="#unittest.mock.Mock.side_effect" title="unittest.mock.Mock.side_effect"><code class="xref py py-attr docutils literal notranslate">side_effect</code></a> attribute. Useful for raising exceptions or
dynamically changing return values. The function is called with the same
arguments as the mock, and unless it returns <a class="reference internal" href="#unittest.mock.DEFAULT" title="unittest.mock.DEFAULT"><code class="xref py py-data docutils literal notranslate">DEFAULT</code></a>, the return
value of this function is used as the return value.
Alternatively side_effect can be an exception class or instance. In
this case the exception will be raised when the mock is called.
If side_effect is an iterable then each call to the mock will return
the next value from the iterable.
A side_effect can be cleared by setting it to <code class="docutils literal notranslate">None</code>.
</li>
<li>return_value: The value returned when the mock is called. By default
this is a new Mock (created on first access). See the
<a class="reference internal" href="#unittest.mock.Mock.return_value" title="unittest.mock.Mock.return_value"><code class="xref py py-attr docutils literal notranslate">return_value</code></a> attribute.
</li>
<li>unsafe: By default if any attribute starts with assert or
assret will raise an <a class="reference internal" href="exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate">AttributeError</code></a>. Passing <code class="docutils literal notranslate">unsafe=True</code>
will allow access to these attributes.
<div class="versionadded">
New in version 3.5.
</div>
</li>
<li>wraps: Item for the mock object to wrap. If wraps is not <code class="docutils literal notranslate">None</code> then
calling the Mock will pass the call through to the wrapped object
(returning the real result). Attribute access on the mock will return a
Mock object that wraps the corresponding attribute of the wrapped
object (so attempting to access an attribute that doesn’t exist will
raise an <a class="reference internal" href="exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate">AttributeError</code></a>).
If the mock has an explicit return_value set then calls are not passed
to the wrapped object and the return_value is returned instead.
</li>
<li>name: If the mock has a name then it will be used in the repr of the
mock. This can be useful for debugging. The name is propagated to child
mocks.
</li>
</ul>
Mocks can also be called with arbitrary keyword arguments. These will be
used to set attributes on the mock after it is created. See the
<a class="reference internal" href="#unittest.mock.Mock.configure_mock" title="unittest.mock.Mock.configure_mock"><code class="xref py py-meth docutils literal notranslate">configure_mock()</code></a> method for details.
<dl class="method">
<dt id="unittest.mock.Mock.assert_called">
<code class="descname">assert_called</code>(*args, **kwargs)<a class="headerlink" href="#unittest.mock.Mock.assert_called" title="Permalink to this definition">¶</a></dt>
<dd>Assert that the mock was called at least once.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock()
&gt;&gt;&gt; mock.method()
&lt;Mock name=&#39;mock.method()&#39; id=&#39;...&#39;&gt;
&gt;&gt;&gt; mock.method.assert_called()
</pre></div>
</div>
<div class="versionadded">
New in version 3.6.
</div>
</dd></dl>

<dl class="method">
<dt id="unittest.mock.Mock.assert_called_once">
<code class="descname">assert_called_once</code>(*args, **kwargs)<a class="headerlink" href="#unittest.mock.Mock.assert_called_once" title="Permalink to this definition">¶</a></dt>
<dd>Assert that the mock was called exactly once.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock()
&gt;&gt;&gt; mock.method()
&lt;Mock name=&#39;mock.method()&#39; id=&#39;...&#39;&gt;
&gt;&gt;&gt; mock.method.assert_called_once()
&gt;&gt;&gt; mock.method()
&lt;Mock name=&#39;mock.method()&#39; id=&#39;...&#39;&gt;
&gt;&gt;&gt; mock.method.assert_called_once()
Traceback (most recent call last):
...
AssertionError: Expected &#39;method&#39; to have been called once. Called 2 times.
</pre></div>
</div>
<div class="versionadded">
New in version 3.6.
</div>
</dd></dl>

<dl class="method">
<dt id="unittest.mock.Mock.assert_called_with">
<code class="descname">assert_called_with</code>(*args, **kwargs)<a class="headerlink" href="#unittest.mock.Mock.assert_called_with" title="Permalink to this definition">¶</a></dt>
<dd>This method is a convenient way of asserting that calls are made in a
particular way:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock()
&gt;&gt;&gt; mock.method(1, 2, 3, test=&#39;wow&#39;)
&lt;Mock name=&#39;mock.method()&#39; id=&#39;...&#39;&gt;
&gt;&gt;&gt; mock.method.assert_called_with(1, 2, 3, test=&#39;wow&#39;)
</pre></div>
</div>
</dd></dl>

<dl class="method">
<dt id="unittest.mock.Mock.assert_called_once_with">
<code class="descname">assert_called_once_with</code>(*args, **kwargs)<a class="headerlink" href="#unittest.mock.Mock.assert_called_once_with" title="Permalink to this definition">¶</a></dt>
<dd>Assert that the mock was called exactly once and that that call was
with the specified arguments.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock(return_value=None)
&gt;&gt;&gt; mock(&#39;foo&#39;, bar=&#39;baz&#39;)
&gt;&gt;&gt; mock.assert_called_once_with(&#39;foo&#39;, bar=&#39;baz&#39;)
&gt;&gt;&gt; mock(&#39;other&#39;, bar=&#39;values&#39;)
&gt;&gt;&gt; mock.assert_called_once_with(&#39;other&#39;, bar=&#39;values&#39;)
Traceback (most recent call last):
 ...
AssertionError: Expected &#39;mock&#39; to be called once. Called 2 times.
</pre></div>
</div>
</dd></dl>

<dl class="method">
<dt id="unittest.mock.Mock.assert_any_call">
<code class="descname">assert_any_call</code>(*args, **kwargs)<a class="headerlink" href="#unittest.mock.Mock.assert_any_call" title="Permalink to this definition">¶</a></dt>
<dd>assert the mock has been called with the specified arguments.
The assert passes if the mock has ever been called, unlike
<a class="reference internal" href="#unittest.mock.Mock.assert_called_with" title="unittest.mock.Mock.assert_called_with"><code class="xref py py-meth docutils literal notranslate">assert_called_with()</code></a> and <a class="reference internal" href="#unittest.mock.Mock.assert_called_once_with" title="unittest.mock.Mock.assert_called_once_with"><code class="xref py py-meth docutils literal notranslate">assert_called_once_with()</code></a> that
only pass if the call is the most recent one, and in the case of
<a class="reference internal" href="#unittest.mock.Mock.assert_called_once_with" title="unittest.mock.Mock.assert_called_once_with"><code class="xref py py-meth docutils literal notranslate">assert_called_once_with()</code></a> it must also be the only call.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock(return_value=None)
&gt;&gt;&gt; mock(1, 2, arg=&#39;thing&#39;)
&gt;&gt;&gt; mock(&#39;some&#39;, &#39;thing&#39;, &#39;else&#39;)
&gt;&gt;&gt; mock.assert_any_call(1, 2, arg=&#39;thing&#39;)
</pre></div>
</div>
</dd></dl>

<dl class="method">
<dt id="unittest.mock.Mock.assert_has_calls">
<code class="descname">assert_has_calls</code>(calls, any_order=False)<a class="headerlink" href="#unittest.mock.Mock.assert_has_calls" title="Permalink to this definition">¶</a></dt>
<dd>assert the mock has been called with the specified calls.
The <a class="reference internal" href="#unittest.mock.Mock.mock_calls" title="unittest.mock.Mock.mock_calls"><code class="xref py py-attr docutils literal notranslate">mock_calls</code></a> list is checked for the calls.
If any_order is false (the default) then the calls must be
sequential. There can be extra calls before or after the
specified calls.
If any_order is true then the calls can be in any order, but
they must all appear in <a class="reference internal" href="#unittest.mock.Mock.mock_calls" title="unittest.mock.Mock.mock_calls"><code class="xref py py-attr docutils literal notranslate">mock_calls</code></a>.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock(return_value=None)
&gt;&gt;&gt; mock(1)
&gt;&gt;&gt; mock(2)
&gt;&gt;&gt; mock(3)
&gt;&gt;&gt; mock(4)
&gt;&gt;&gt; calls = [call(2), call(3)]
&gt;&gt;&gt; mock.assert_has_calls(calls)
&gt;&gt;&gt; calls = [call(4), call(2), call(3)]
&gt;&gt;&gt; mock.assert_has_calls(calls, any_order=True)
</pre></div>
</div>
</dd></dl>

<dl class="method">
<dt id="unittest.mock.Mock.assert_not_called">
<code class="descname">assert_not_called</code>()<a class="headerlink" href="#unittest.mock.Mock.assert_not_called" title="Permalink to this definition">¶</a></dt>
<dd>Assert the mock was never called.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; m = Mock()
&gt;&gt;&gt; m.hello.assert_not_called()
&gt;&gt;&gt; obj = m.hello()
&gt;&gt;&gt; m.hello.assert_not_called()
Traceback (most recent call last):
 ...
AssertionError: Expected &#39;hello&#39; to not have been called. Called 1 times.
</pre></div>
</div>
<div class="versionadded">
New in version 3.5.
</div>
</dd></dl>

<dl class="method">
<dt id="unittest.mock.Mock.reset_mock">
<code class="descname">reset_mock</code>(*, return_value=False, side_effect=False)<a class="headerlink" href="#unittest.mock.Mock.reset_mock" title="Permalink to this definition">¶</a></dt>
<dd>The reset_mock method resets all the call attributes on a mock object:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock(return_value=None)
&gt;&gt;&gt; mock(&#39;hello&#39;)
&gt;&gt;&gt; mock.called
True
&gt;&gt;&gt; mock.reset_mock()
&gt;&gt;&gt; mock.called
False
</pre></div>
</div>
<div class="versionchanged">
Changed in version 3.6: Added two keyword only argument to the reset_mock function.
</div>
This can be useful where you want to make a series of assertions that
reuse the same object. Note that <a class="reference internal" href="#unittest.mock.Mock.reset_mock" title="unittest.mock.Mock.reset_mock"><code class="xref py py-meth docutils literal notranslate">reset_mock()</code></a> doesn’t clear the
return value, <a class="reference internal" href="#unittest.mock.Mock.side_effect" title="unittest.mock.Mock.side_effect"><code class="xref py py-attr docutils literal notranslate">side_effect</code></a> or any child attributes you have
set using normal assignment by default. In case you want to reset
return_value or <a class="reference internal" href="#unittest.mock.Mock.side_effect" title="unittest.mock.Mock.side_effect"><code class="xref py py-attr docutils literal notranslate">side_effect</code></a>, then pass the corresponding
parameter as <code class="docutils literal notranslate">True</code>. Child mocks and the return value mock
(if any) are reset as well.
<div class="admonition note">
Note
return_value, and <a class="reference internal" href="#unittest.mock.Mock.side_effect" title="unittest.mock.Mock.side_effect"><code class="xref py py-attr docutils literal notranslate">side_effect</code></a> are keyword only
argument.
</div>
</dd></dl>

<dl class="method">
<dt id="unittest.mock.Mock.mock_add_spec">
<code class="descname">mock_add_spec</code>(spec, spec_set=False)<a class="headerlink" href="#unittest.mock.Mock.mock_add_spec" title="Permalink to this definition">¶</a></dt>
<dd>Add a spec to a mock. spec can either be an object or a
list of strings. Only attributes on the spec can be fetched as
attributes from the mock.
If spec_set is true then only attributes on the spec can be set.
</dd></dl>

<dl class="method">
<dt id="unittest.mock.Mock.attach_mock">
<code class="descname">attach_mock</code>(mock, attribute)<a class="headerlink" href="#unittest.mock.Mock.attach_mock" title="Permalink to this definition">¶</a></dt>
<dd>Attach a mock as an attribute of this one, replacing its name and
parent. Calls to the attached mock will be recorded in the
<a class="reference internal" href="#unittest.mock.Mock.method_calls" title="unittest.mock.Mock.method_calls"><code class="xref py py-attr docutils literal notranslate">method_calls</code></a> and <a class="reference internal" href="#unittest.mock.Mock.mock_calls" title="unittest.mock.Mock.mock_calls"><code class="xref py py-attr docutils literal notranslate">mock_calls</code></a> attributes of this one.
</dd></dl>

<dl class="method">
<dt id="unittest.mock.Mock.configure_mock">
<code class="descname">configure_mock</code>(**kwargs)<a class="headerlink" href="#unittest.mock.Mock.configure_mock" title="Permalink to this definition">¶</a></dt>
<dd>Set attributes on the mock through keyword arguments.
Attributes plus return values and side effects can be set on child
mocks using standard dot notation and unpacking a dictionary in the
method call:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock()
&gt;&gt;&gt; attrs = {&#39;method.return_value&#39;: 3, &#39;other.side_effect&#39;: KeyError}
&gt;&gt;&gt; mock.configure_mock(**attrs)
&gt;&gt;&gt; mock.method()
3
&gt;&gt;&gt; mock.other()
Traceback (most recent call last):
 ...
KeyError
</pre></div>
</div>
The same thing can be achieved in the constructor call to mocks:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; attrs = {&#39;method.return_value&#39;: 3, &#39;other.side_effect&#39;: KeyError}
&gt;&gt;&gt; mock = Mock(some_attribute=&#39;eggs&#39;, **attrs)
&gt;&gt;&gt; mock.some_attribute
&#39;eggs&#39;
&gt;&gt;&gt; mock.method()
3
&gt;&gt;&gt; mock.other()
Traceback (most recent call last):
 ...
KeyError
</pre></div>
</div>
<a class="reference internal" href="#unittest.mock.Mock.configure_mock" title="unittest.mock.Mock.configure_mock"><code class="xref py py-meth docutils literal notranslate">configure_mock()</code></a> exists to make it easier to do configuration
after the mock has been created.
</dd></dl>

<dl class="method">
<dt id="unittest.mock.Mock.__dir__">
<code class="descname">__dir__</code>()<a class="headerlink" href="#unittest.mock.Mock.__dir__" title="Permalink to this definition">¶</a></dt>
<dd><a class="reference internal" href="#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate">Mock</code></a> objects limit the results of <code class="docutils literal notranslate">dir(some_mock)</code> to useful results.
For mocks with a spec this includes all the permitted attributes
for the mock.
See <a class="reference internal" href="#unittest.mock.FILTER_DIR" title="unittest.mock.FILTER_DIR"><code class="xref py py-data docutils literal notranslate">FILTER_DIR</code></a> for what this filtering does, and how to
switch it off.
</dd></dl>

<dl class="method">
<dt id="unittest.mock.Mock._get_child_mock">
<code class="descname">_get_child_mock</code>(**kw)<a class="headerlink" href="#unittest.mock.Mock._get_child_mock" title="Permalink to this definition">¶</a></dt>
<dd>Create the child mocks for attributes and return value.
By default child mocks will be the same type as the parent.
Subclasses of Mock may want to override this to customize the way
child mocks are made.
For non-callable mocks the callable variant will be used (rather than
any custom subclass).
</dd></dl>

<dl class="attribute">
<dt id="unittest.mock.Mock.called">
<code class="descname">called</code><a class="headerlink" href="#unittest.mock.Mock.called" title="Permalink to this definition">¶</a></dt>
<dd>A boolean representing whether or not the mock object has been called:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock(return_value=None)
&gt;&gt;&gt; mock.called
False
&gt;&gt;&gt; mock()
&gt;&gt;&gt; mock.called
True
</pre></div>
</div>
</dd></dl>

<dl class="attribute">
<dt id="unittest.mock.Mock.call_count">
<code class="descname">call_count</code><a class="headerlink" href="#unittest.mock.Mock.call_count" title="Permalink to this definition">¶</a></dt>
<dd>An integer telling you how many times the mock object has been called:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock(return_value=None)
&gt;&gt;&gt; mock.call_count
0
&gt;&gt;&gt; mock()
&gt;&gt;&gt; mock()
&gt;&gt;&gt; mock.call_count
2
</pre></div>
</div>
</dd></dl>

<dl class="attribute">
<dt id="unittest.mock.Mock.return_value">
<code class="descname">return_value</code><a class="headerlink" href="#unittest.mock.Mock.return_value" title="Permalink to this definition">¶</a></dt>
<dd>Set this to configure the value returned by calling the mock:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock()
&gt;&gt;&gt; mock.return_value = &#39;fish&#39;
&gt;&gt;&gt; mock()
&#39;fish&#39;
</pre></div>
</div>
The default return value is a mock object and you can configure it in
the normal way:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock()
&gt;&gt;&gt; mock.return_value.attribute = sentinel.Attribute
&gt;&gt;&gt; mock.return_value()
&lt;Mock name=&#39;mock()()&#39; id=&#39;...&#39;&gt;
&gt;&gt;&gt; mock.return_value.assert_called_with()
</pre></div>
</div>
<a class="reference internal" href="#unittest.mock.Mock.return_value" title="unittest.mock.Mock.return_value"><code class="xref py py-attr docutils literal notranslate">return_value</code></a> can also be set in the constructor:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock(return_value=3)
&gt;&gt;&gt; mock.return_value
3
&gt;&gt;&gt; mock()
3
</pre></div>
</div>
</dd></dl>

<dl class="attribute">
<dt id="unittest.mock.Mock.side_effect">
<code class="descname">side_effect</code><a class="headerlink" href="#unittest.mock.Mock.side_effect" title="Permalink to this definition">¶</a></dt>
<dd>This can either be a function to be called when the mock is called,
an iterable or an exception (class or instance) to be raised.
If you pass in a function it will be called with same arguments as the
mock and unless the function returns the <a class="reference internal" href="#unittest.mock.DEFAULT" title="unittest.mock.DEFAULT"><code class="xref py py-data docutils literal notranslate">DEFAULT</code></a> singleton the
call to the mock will then return whatever the function returns. If the
function returns <a class="reference internal" href="#unittest.mock.DEFAULT" title="unittest.mock.DEFAULT"><code class="xref py py-data docutils literal notranslate">DEFAULT</code></a> then the mock will return its normal
value (from the <a class="reference internal" href="#unittest.mock.Mock.return_value" title="unittest.mock.Mock.return_value"><code class="xref py py-attr docutils literal notranslate">return_value</code></a>).
If you pass in an iterable, it is used to retrieve an iterator which
must yield a value on every call. This value can either be an exception
instance to be raised, or a value to be returned from the call to the
mock (<a class="reference internal" href="#unittest.mock.DEFAULT" title="unittest.mock.DEFAULT"><code class="xref py py-data docutils literal notranslate">DEFAULT</code></a> handling is identical to the function case).
An example of a mock that raises an exception (to test exception
handling of an API):
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock()
&gt;&gt;&gt; mock.side_effect = Exception(&#39;Boom!&#39;)
&gt;&gt;&gt; mock()
Traceback (most recent call last):
 ...
Exception: Boom!
</pre></div>
</div>
Using <a class="reference internal" href="#unittest.mock.Mock.side_effect" title="unittest.mock.Mock.side_effect"><code class="xref py py-attr docutils literal notranslate">side_effect</code></a> to return a sequence of values:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock()
&gt;&gt;&gt; mock.side_effect = [3, 2, 1]
&gt;&gt;&gt; mock(), mock(), mock()
(3, 2, 1)
</pre></div>
</div>
Using a callable:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock(return_value=3)
&gt;&gt;&gt; def side_effect(*args, **kwargs):
... return DEFAULT
...
&gt;&gt;&gt; mock.side_effect = side_effect
&gt;&gt;&gt; mock()
3
</pre></div>
</div>
<a class="reference internal" href="#unittest.mock.Mock.side_effect" title="unittest.mock.Mock.side_effect"><code class="xref py py-attr docutils literal notranslate">side_effect</code></a> can be set in the constructor. Here’s an example that
adds one to the value the mock is called with and returns it:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; side_effect = lambda value: value + 1
&gt;&gt;&gt; mock = Mock(side_effect=side_effect)
&gt;&gt;&gt; mock(3)
4
&gt;&gt;&gt; mock(-8)
-7
</pre></div>
</div>
Setting <a class="reference internal" href="#unittest.mock.Mock.side_effect" title="unittest.mock.Mock.side_effect"><code class="xref py py-attr docutils literal notranslate">side_effect</code></a> to <code class="docutils literal notranslate">None</code> clears it:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; m = Mock(side_effect=KeyError, return_value=3)
&gt;&gt;&gt; m()
Traceback (most recent call last):
 ...
KeyError
&gt;&gt;&gt; m.side_effect = None
&gt;&gt;&gt; m()
3
</pre></div>
</div>
</dd></dl>

<dl class="attribute">
<dt id="unittest.mock.Mock.call_args">
<code class="descname">call_args</code><a class="headerlink" href="#unittest.mock.Mock.call_args" title="Permalink to this definition">¶</a></dt>
<dd>This is either <code class="docutils literal notranslate">None</code> (if the mock hasn’t been called), or the
arguments that the mock was last called with. This will be in the
form of a tuple: the first member is any ordered arguments the mock
was called with (or an empty tuple) and the second member is any
keyword arguments (or an empty dictionary).
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock(return_value=None)
&gt;&gt;&gt; print(mock.call_args)
None
&gt;&gt;&gt; mock()
&gt;&gt;&gt; mock.call_args
call()
&gt;&gt;&gt; mock.call_args == ()
True
&gt;&gt;&gt; mock(3, 4)
&gt;&gt;&gt; mock.call_args
call(3, 4)
&gt;&gt;&gt; mock.call_args == ((3, 4),)
True
&gt;&gt;&gt; mock(3, 4, 5, key=&#39;fish&#39;, next=&#39;w00t!&#39;)
&gt;&gt;&gt; mock.call_args
call(3, 4, 5, key=&#39;fish&#39;, next=&#39;w00t!&#39;)
</pre></div>
</div>
<a class="reference internal" href="#unittest.mock.Mock.call_args" title="unittest.mock.Mock.call_args"><code class="xref py py-attr docutils literal notranslate">call_args</code></a>, along with members of the lists <a class="reference internal" href="#unittest.mock.Mock.call_args_list" title="unittest.mock.Mock.call_args_list"><code class="xref py py-attr docutils literal notranslate">call_args_list</code></a>,
<a class="reference internal" href="#unittest.mock.Mock.method_calls" title="unittest.mock.Mock.method_calls"><code class="xref py py-attr docutils literal notranslate">method_calls</code></a> and <a class="reference internal" href="#unittest.mock.Mock.mock_calls" title="unittest.mock.Mock.mock_calls"><code class="xref py py-attr docutils literal notranslate">mock_calls</code></a> are <a class="reference internal" href="#unittest.mock.call" title="unittest.mock.call"><code class="xref py py-data docutils literal notranslate">call</code></a> objects.
These are tuples, so they can be unpacked to get at the individual
arguments and make more complex assertions. See
<a class="reference internal" href="#calls-as-tuples">calls as tuples</a>.
</dd></dl>

<dl class="attribute">
<dt id="unittest.mock.Mock.call_args_list">
<code class="descname">call_args_list</code><a class="headerlink" href="#unittest.mock.Mock.call_args_list" title="Permalink to this definition">¶</a></dt>
<dd>This is a list of all the calls made to the mock object in sequence
(so the length of the list is the number of times it has been
called). Before any calls have been made it is an empty list. The
<a class="reference internal" href="#unittest.mock.call" title="unittest.mock.call"><code class="xref py py-data docutils literal notranslate">call</code></a> object can be used for conveniently constructing lists of
calls to compare with <a class="reference internal" href="#unittest.mock.Mock.call_args_list" title="unittest.mock.Mock.call_args_list"><code class="xref py py-attr docutils literal notranslate">call_args_list</code></a>.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock(return_value=None)
&gt;&gt;&gt; mock()
&gt;&gt;&gt; mock(3, 4)
&gt;&gt;&gt; mock(key=&#39;fish&#39;, next=&#39;w00t!&#39;)
&gt;&gt;&gt; mock.call_args_list
[call(), call(3, 4), call(key=&#39;fish&#39;, next=&#39;w00t!&#39;)]
&gt;&gt;&gt; expected = [(), ((3, 4),), ({&#39;key&#39;: &#39;fish&#39;, &#39;next&#39;: &#39;w00t!&#39;},)]
&gt;&gt;&gt; mock.call_args_list == expected
True
</pre></div>
</div>
Members of <a class="reference internal" href="#unittest.mock.Mock.call_args_list" title="unittest.mock.Mock.call_args_list"><code class="xref py py-attr docutils literal notranslate">call_args_list</code></a> are <a class="reference internal" href="#unittest.mock.call" title="unittest.mock.call"><code class="xref py py-data docutils literal notranslate">call</code></a> objects. These can be
unpacked as tuples to get at the individual arguments. See
<a class="reference internal" href="#calls-as-tuples">calls as tuples</a>.
</dd></dl>

<dl class="attribute">
<dt id="unittest.mock.Mock.method_calls">
<code class="descname">method_calls</code><a class="headerlink" href="#unittest.mock.Mock.method_calls" title="Permalink to this definition">¶</a></dt>
<dd>As well as tracking calls to themselves, mocks also track calls to
methods and attributes, and their methods and attributes:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock()
&gt;&gt;&gt; mock.method()
&lt;Mock name=&#39;mock.method()&#39; id=&#39;...&#39;&gt;
&gt;&gt;&gt; mock.property.method.attribute()
&lt;Mock name=&#39;mock.property.method.attribute()&#39; id=&#39;...&#39;&gt;
&gt;&gt;&gt; mock.method_calls
[call.method(), call.property.method.attribute()]
</pre></div>
</div>
Members of <a class="reference internal" href="#unittest.mock.Mock.method_calls" title="unittest.mock.Mock.method_calls"><code class="xref py py-attr docutils literal notranslate">method_calls</code></a> are <a class="reference internal" href="#unittest.mock.call" title="unittest.mock.call"><code class="xref py py-data docutils literal notranslate">call</code></a> objects. These can be
unpacked as tuples to get at the individual arguments. See
<a class="reference internal" href="#calls-as-tuples">calls as tuples</a>.
</dd></dl>

<dl class="attribute">
<dt id="unittest.mock.Mock.mock_calls">
<code class="descname">mock_calls</code><a class="headerlink" href="#unittest.mock.Mock.mock_calls" title="Permalink to this definition">¶</a></dt>
<dd><a class="reference internal" href="#unittest.mock.Mock.mock_calls" title="unittest.mock.Mock.mock_calls"><code class="xref py py-attr docutils literal notranslate">mock_calls</code></a> records all calls to the mock object, its methods,
magic methods and return value mocks.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = MagicMock()
&gt;&gt;&gt; result = mock(1, 2, 3)
&gt;&gt;&gt; mock.first(a=3)
&lt;MagicMock name=&#39;mock.first()&#39; id=&#39;...&#39;&gt;
&gt;&gt;&gt; mock.second()
&lt;MagicMock name=&#39;mock.second()&#39; id=&#39;...&#39;&gt;
&gt;&gt;&gt; int(mock)
1
&gt;&gt;&gt; result(1)
&lt;MagicMock name=&#39;mock()()&#39; id=&#39;...&#39;&gt;
&gt;&gt;&gt; expected = [call(1, 2, 3), call.first(a=3), call.second(),
... call.__int__(), call()(1)]
&gt;&gt;&gt; mock.mock_calls == expected
True
</pre></div>
</div>
Members of <a class="reference internal" href="#unittest.mock.Mock.mock_calls" title="unittest.mock.Mock.mock_calls"><code class="xref py py-attr docutils literal notranslate">mock_calls</code></a> are <a class="reference internal" href="#unittest.mock.call" title="unittest.mock.call"><code class="xref py py-data docutils literal notranslate">call</code></a> objects. These can be
unpacked as tuples to get at the individual arguments. See
<a class="reference internal" href="#calls-as-tuples">calls as tuples</a>.
</dd></dl>

<dl class="attribute">
<dt id="unittest.mock.Mock.__class__">
<code class="descname">__class__</code><a class="headerlink" href="#unittest.mock.Mock.__class__" title="Permalink to this definition">¶</a></dt>
<dd>Normally the <a class="reference internal" href="#unittest.mock.Mock.__class__" title="unittest.mock.Mock.__class__"><code class="xref py py-attr docutils literal notranslate">__class__</code></a> attribute of an object will return its type.
For a mock object with a <code class="xref py py-attr docutils literal notranslate">spec</code>, <code class="docutils literal notranslate">__class__</code> returns the spec class
instead. This allows mock objects to pass <a class="reference internal" href="functions.html#isinstance" title="isinstance"><code class="xref py py-func docutils literal notranslate">isinstance()</code></a> tests for the
object they are replacing / masquerading as:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock(spec=3)
&gt;&gt;&gt; isinstance(mock, int)
True
</pre></div>
</div>
<a class="reference internal" href="#unittest.mock.Mock.__class__" title="unittest.mock.Mock.__class__"><code class="xref py py-attr docutils literal notranslate">__class__</code></a> is assignable to, this allows a mock to pass an
<a class="reference internal" href="functions.html#isinstance" title="isinstance"><code class="xref py py-func docutils literal notranslate">isinstance()</code></a> check without forcing you to use a spec:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock()
&gt;&gt;&gt; mock.__class__ = dict
&gt;&gt;&gt; isinstance(mock, dict)
True
</pre></div>
</div>
</dd></dl>

</dd></dl>

<dl class="class">
<dt id="unittest.mock.NonCallableMock">
class <code class="descclassname">unittest.mock.</code><code class="descname">NonCallableMock</code>(spec=None, wraps=None, name=None, spec_set=None, **kwargs)<a class="headerlink" href="#unittest.mock.NonCallableMock" title="Permalink to this definition">¶</a></dt>
<dd>A non-callable version of <a class="reference internal" href="#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate">Mock</code></a>. The constructor parameters have the same
meaning of <a class="reference internal" href="#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate">Mock</code></a>, with the exception of return_value and side_effect
which have no meaning on a non-callable mock.
</dd></dl>

Mock objects that use a class or an instance as a <code class="xref py py-attr docutils literal notranslate">spec</code> or
<code class="xref py py-attr docutils literal notranslate">spec_set</code> are able to pass <a class="reference internal" href="functions.html#isinstance" title="isinstance"><code class="xref py py-func docutils literal notranslate">isinstance()</code></a> tests:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock(spec=SomeClass)
&gt;&gt;&gt; isinstance(mock, SomeClass)
True
&gt;&gt;&gt; mock = Mock(spec_set=SomeClass())
&gt;&gt;&gt; isinstance(mock, SomeClass)
True
</pre></div>
</div>
The <a class="reference internal" href="#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate">Mock</code></a> classes have support for mocking magic methods. See <a class="reference internal" href="#magic-methods">magic
methods</a> for the full details.
The mock classes and the <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> decorators all take arbitrary keyword
arguments for configuration. For the <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> decorators the keywords are
passed to the constructor of the mock being created. The keyword arguments
are for configuring attributes of the mock:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; m = MagicMock(attribute=3, other=&#39;fish&#39;)
&gt;&gt;&gt; m.attribute
3
&gt;&gt;&gt; m.other
&#39;fish&#39;
</pre></div>
</div>
The return value and side effect of child mocks can be set in the same way,
using dotted notation. As you can’t use dotted names directly in a call you
have to create a dictionary and unpack it using <code class="docutils literal notranslate">**</code>:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; attrs = {&#39;method.return_value&#39;: 3, &#39;other.side_effect&#39;: KeyError}
&gt;&gt;&gt; mock = Mock(some_attribute=&#39;eggs&#39;, **attrs)
&gt;&gt;&gt; mock.some_attribute
&#39;eggs&#39;
&gt;&gt;&gt; mock.method()
3
&gt;&gt;&gt; mock.other()
Traceback (most recent call last):
 ...
KeyError
</pre></div>
</div>
A callable mock which was created with a spec (or a spec_set) will
introspect the specification object’s signature when matching calls to
the mock. Therefore, it can match the actual call’s arguments regardless
of whether they were passed positionally or by name:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; def f(a, b, c): pass
...
&gt;&gt;&gt; mock = Mock(spec=f)
&gt;&gt;&gt; mock(1, 2, c=3)
&lt;Mock name=&#39;mock()&#39; id=&#39;140161580456576&#39;&gt;
&gt;&gt;&gt; mock.assert_called_with(1, 2, 3)
&gt;&gt;&gt; mock.assert_called_with(a=1, b=2, c=3)
</pre></div>
</div>
This applies to <a class="reference internal" href="#unittest.mock.Mock.assert_called_with" title="unittest.mock.Mock.assert_called_with"><code class="xref py py-meth docutils literal notranslate">assert_called_with()</code></a>,
<a class="reference internal" href="#unittest.mock.Mock.assert_called_once_with" title="unittest.mock.Mock.assert_called_once_with"><code class="xref py py-meth docutils literal notranslate">assert_called_once_with()</code></a>, <a class="reference internal" href="#unittest.mock.Mock.assert_has_calls" title="unittest.mock.Mock.assert_has_calls"><code class="xref py py-meth docutils literal notranslate">assert_has_calls()</code></a> and
<a class="reference internal" href="#unittest.mock.Mock.assert_any_call" title="unittest.mock.Mock.assert_any_call"><code class="xref py py-meth docutils literal notranslate">assert_any_call()</code></a>. When <a class="reference internal" href="#auto-speccing">Autospeccing</a>, it will also
apply to method calls on the mock object.
<blockquote>
<div><div class="versionchanged">
Changed in version 3.4: Added signature introspection on specced and autospecced mock objects.
</div>
</div></blockquote>
<dl class="class">
<dt id="unittest.mock.PropertyMock">
class <code class="descclassname">unittest.mock.</code><code class="descname">PropertyMock</code>(*args, **kwargs)<a class="headerlink" href="#unittest.mock.PropertyMock" title="Permalink to this definition">¶</a></dt>
<dd>A mock intended to be used as a property, or other descriptor, on a class.
<a class="reference internal" href="#unittest.mock.PropertyMock" title="unittest.mock.PropertyMock"><code class="xref py py-class docutils literal notranslate">PropertyMock</code></a> provides <a class="reference internal" href="../reference/datamodel.html#object.__get__" title="object.__get__"><code class="xref py py-meth docutils literal notranslate">__get__()</code></a> and <a class="reference internal" href="../reference/datamodel.html#object.__set__" title="object.__set__"><code class="xref py py-meth docutils literal notranslate">__set__()</code></a> methods
so you can specify a return value when it is fetched.
Fetching a <a class="reference internal" href="#unittest.mock.PropertyMock" title="unittest.mock.PropertyMock"><code class="xref py py-class docutils literal notranslate">PropertyMock</code></a> instance from an object calls the mock, with
no args. Setting it calls the mock with the value being set.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class Foo:
... @property
... def foo(self):
... return &#39;something&#39;
... @foo.setter
... def foo(self, value):
... pass
...
&gt;&gt;&gt; with patch(&#39;__main__.Foo.foo&#39;, new_callable=PropertyMock) as mock_foo:
... mock_foo.return_value = &#39;mockity-mock&#39;
... this_foo = Foo()
... print(this_foo.foo)
... this_foo.foo = 6
...
mockity-mock
&gt;&gt;&gt; mock_foo.mock_calls
[call(), call(6)]
</pre></div>
</div>
</dd></dl>

Because of the way mock attributes are stored you can’t directly attach a
<a class="reference internal" href="#unittest.mock.PropertyMock" title="unittest.mock.PropertyMock"><code class="xref py py-class docutils literal notranslate">PropertyMock</code></a> to a mock object. Instead you can attach it to the mock type
object:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; m = MagicMock()
&gt;&gt;&gt; p = PropertyMock(return_value=3)
&gt;&gt;&gt; type(m).foo = p
&gt;&gt;&gt; m.foo
3
&gt;&gt;&gt; p.assert_called_once_with()
</pre></div>
</div>
<div class="section" id="calling">
<h3>26.5.2.1. Calling<a class="headerlink" href="#calling" title="Permalink to this headline">¶</a></h3>
Mock objects are callable. The call will return the value set as the
<a class="reference internal" href="#unittest.mock.Mock.return_value" title="unittest.mock.Mock.return_value"><code class="xref py py-attr docutils literal notranslate">return_value</code></a> attribute. The default return value is a new Mock
object; it is created the first time the return value is accessed (either
explicitly or by calling the Mock) - but it is stored and the same one
returned each time.
Calls made to the object will be recorded in the attributes
like <a class="reference internal" href="#unittest.mock.Mock.call_args" title="unittest.mock.Mock.call_args"><code class="xref py py-attr docutils literal notranslate">call_args</code></a> and <a class="reference internal" href="#unittest.mock.Mock.call_args_list" title="unittest.mock.Mock.call_args_list"><code class="xref py py-attr docutils literal notranslate">call_args_list</code></a>.
If <a class="reference internal" href="#unittest.mock.Mock.side_effect" title="unittest.mock.Mock.side_effect"><code class="xref py py-attr docutils literal notranslate">side_effect</code></a> is set then it will be called after the call has
been recorded, so if <code class="xref py py-attr docutils literal notranslate">side_effect</code> raises an exception the call is still
recorded.
The simplest way to make a mock raise an exception when called is to make
<a class="reference internal" href="#unittest.mock.Mock.side_effect" title="unittest.mock.Mock.side_effect"><code class="xref py py-attr docutils literal notranslate">side_effect</code></a> an exception class or instance:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; m = MagicMock(side_effect=IndexError)
&gt;&gt;&gt; m(1, 2, 3)
Traceback (most recent call last):
 ...
IndexError
&gt;&gt;&gt; m.mock_calls
[call(1, 2, 3)]
&gt;&gt;&gt; m.side_effect = KeyError(&#39;Bang!&#39;)
&gt;&gt;&gt; m(&#39;two&#39;, &#39;three&#39;, &#39;four&#39;)
Traceback (most recent call last):
 ...
KeyError: &#39;Bang!&#39;
&gt;&gt;&gt; m.mock_calls
[call(1, 2, 3), call(&#39;two&#39;, &#39;three&#39;, &#39;four&#39;)]
</pre></div>
</div>
If <code class="xref py py-attr docutils literal notranslate">side_effect</code> is a function then whatever that function returns is what
calls to the mock return. The <code class="xref py py-attr docutils literal notranslate">side_effect</code> function is called with the
same arguments as the mock. This allows you to vary the return value of the
call dynamically, based on the input:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; def side_effect(value):
... return value + 1
...
&gt;&gt;&gt; m = MagicMock(side_effect=side_effect)
&gt;&gt;&gt; m(1)
2
&gt;&gt;&gt; m(2)
3
&gt;&gt;&gt; m.mock_calls
[call(1), call(2)]
</pre></div>
</div>
If you want the mock to still return the default return value (a new mock), or
any set return value, then there are two ways of doing this. Either return
<code class="xref py py-attr docutils literal notranslate">mock.return_value</code> from inside <code class="xref py py-attr docutils literal notranslate">side_effect</code>, or return <a class="reference internal" href="#unittest.mock.DEFAULT" title="unittest.mock.DEFAULT"><code class="xref py py-data docutils literal notranslate">DEFAULT</code></a>:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; m = MagicMock()
&gt;&gt;&gt; def side_effect(*args, **kwargs):
... return m.return_value
...
&gt;&gt;&gt; m.side_effect = side_effect
&gt;&gt;&gt; m.return_value = 3
&gt;&gt;&gt; m()
3
&gt;&gt;&gt; def side_effect(*args, **kwargs):
... return DEFAULT
...
&gt;&gt;&gt; m.side_effect = side_effect
&gt;&gt;&gt; m()
3
</pre></div>
</div>
To remove a <code class="xref py py-attr docutils literal notranslate">side_effect</code>, and return to the default behaviour, set the
<code class="xref py py-attr docutils literal notranslate">side_effect</code> to <code class="docutils literal notranslate">None</code>:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; m = MagicMock(return_value=6)
&gt;&gt;&gt; def side_effect(*args, **kwargs):
... return 3
...
&gt;&gt;&gt; m.side_effect = side_effect
&gt;&gt;&gt; m()
3
&gt;&gt;&gt; m.side_effect = None
&gt;&gt;&gt; m()
6
</pre></div>
</div>
The <code class="xref py py-attr docutils literal notranslate">side_effect</code> can also be any iterable object. Repeated calls to the mock
will return values from the iterable (until the iterable is exhausted and
a <a class="reference internal" href="exceptions.html#StopIteration" title="StopIteration"><code class="xref py py-exc docutils literal notranslate">StopIteration</code></a> is raised):
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; m = MagicMock(side_effect=[1, 2, 3])
&gt;&gt;&gt; m()
1
&gt;&gt;&gt; m()
2
&gt;&gt;&gt; m()
3
&gt;&gt;&gt; m()
Traceback (most recent call last):
 ...
StopIteration
</pre></div>
</div>
If any members of the iterable are exceptions they will be raised instead of
returned:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; iterable = (33, ValueError, 66)
&gt;&gt;&gt; m = MagicMock(side_effect=iterable)
&gt;&gt;&gt; m()
33
&gt;&gt;&gt; m()
Traceback (most recent call last):
 ...
ValueError
&gt;&gt;&gt; m()
66
</pre></div>
</div>
</div>
<div class="section" id="deleting-attributes">
<h3>26.5.2.2. Deleting Attributes<a class="headerlink" href="#deleting-attributes" title="Permalink to this headline">¶</a></h3>
Mock objects create attributes on demand. This allows them to pretend to be
objects of any type.
You may want a mock object to return <code class="docutils literal notranslate">False</code> to a <a class="reference internal" href="functions.html#hasattr" title="hasattr"><code class="xref py py-func docutils literal notranslate">hasattr()</code></a> call, or raise an
<a class="reference internal" href="exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate">AttributeError</code></a> when an attribute is fetched. You can do this by providing
an object as a <code class="xref py py-attr docutils literal notranslate">spec</code> for a mock, but that isn’t always convenient.
You “block” attributes by deleting them. Once deleted, accessing an attribute
will raise an <a class="reference internal" href="exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate">AttributeError</code></a>.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = MagicMock()
&gt;&gt;&gt; hasattr(mock, &#39;m&#39;)
True
&gt;&gt;&gt; del mock.m
&gt;&gt;&gt; hasattr(mock, &#39;m&#39;)
False
&gt;&gt;&gt; del mock.f
&gt;&gt;&gt; mock.f
Traceback (most recent call last):
 ...
AttributeError: f
</pre></div>
</div>
</div>
<div class="section" id="mock-names-and-the-name-attribute">
<h3>26.5.2.3. Mock names and the name attribute<a class="headerlink" href="#mock-names-and-the-name-attribute" title="Permalink to this headline">¶</a></h3>
Since “name” is an argument to the <a class="reference internal" href="#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate">Mock</code></a> constructor, if you want your
mock object to have a “name” attribute you can’t just pass it in at creation
time. There are two alternatives. One option is to use
<a class="reference internal" href="#unittest.mock.Mock.configure_mock" title="unittest.mock.Mock.configure_mock"><code class="xref py py-meth docutils literal notranslate">configure_mock()</code></a>:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = MagicMock()
&gt;&gt;&gt; mock.configure_mock(name=&#39;my_name&#39;)
&gt;&gt;&gt; mock.name
&#39;my_name&#39;
</pre></div>
</div>
A simpler option is to simply set the “name” attribute after mock creation:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = MagicMock()
&gt;&gt;&gt; mock.name = &quot;foo&quot;
</pre></div>
</div>
</div>
<div class="section" id="attaching-mocks-as-attributes">
<h3>26.5.2.4. Attaching Mocks as Attributes<a class="headerlink" href="#attaching-mocks-as-attributes" title="Permalink to this headline">¶</a></h3>
When you attach a mock as an attribute of another mock (or as the return
value) it becomes a “child” of that mock. Calls to the child are recorded in
the <a class="reference internal" href="#unittest.mock.Mock.method_calls" title="unittest.mock.Mock.method_calls"><code class="xref py py-attr docutils literal notranslate">method_calls</code></a> and <a class="reference internal" href="#unittest.mock.Mock.mock_calls" title="unittest.mock.Mock.mock_calls"><code class="xref py py-attr docutils literal notranslate">mock_calls</code></a> attributes of the
parent. This is useful for configuring child mocks and then attaching them to
the parent, or for attaching mocks to a parent that records all calls to the
children and allows you to make assertions about the order of calls between
mocks:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; parent = MagicMock()
&gt;&gt;&gt; child1 = MagicMock(return_value=None)
&gt;&gt;&gt; child2 = MagicMock(return_value=None)
&gt;&gt;&gt; parent.child1 = child1
&gt;&gt;&gt; parent.child2 = child2
&gt;&gt;&gt; child1(1)
&gt;&gt;&gt; child2(2)
&gt;&gt;&gt; parent.mock_calls
[call.child1(1), call.child2(2)]
</pre></div>
</div>
The exception to this is if the mock has a name. This allows you to prevent
the “parenting” if for some reason you don’t want it to happen.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = MagicMock()
&gt;&gt;&gt; not_a_child = MagicMock(name=&#39;not-a-child&#39;)
&gt;&gt;&gt; mock.attribute = not_a_child
&gt;&gt;&gt; mock.attribute()
&lt;MagicMock name=&#39;not-a-child()&#39; id=&#39;...&#39;&gt;
&gt;&gt;&gt; mock.mock_calls
[]
</pre></div>
</div>
Mocks created for you by <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> are automatically given names. To
attach mocks that have names to a parent you use the <a class="reference internal" href="#unittest.mock.Mock.attach_mock" title="unittest.mock.Mock.attach_mock"><code class="xref py py-meth docutils literal notranslate">attach_mock()</code></a>
method:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; thing1 = object()
&gt;&gt;&gt; thing2 = object()
&gt;&gt;&gt; parent = MagicMock()
&gt;&gt;&gt; with patch(&#39;__main__.thing1&#39;, return_value=None) as child1:
... with patch(&#39;__main__.thing2&#39;, return_value=None) as child2:
... parent.attach_mock(child1, &#39;child1&#39;)
... parent.attach_mock(child2, &#39;child2&#39;)
... child1(&#39;one&#39;)
... child2(&#39;two&#39;)
...
&gt;&gt;&gt; parent.mock_calls
[call.child1(&#39;one&#39;), call.child2(&#39;two&#39;)]
</pre></div>
</div>
<table class="docutils footnote" frame="void" id="id3" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id1">[1]</a></td><td>The only exceptions are magic methods and attributes (those that have
leading and trailing double underscores). Mock doesn’t create these but
instead raises an <a class="reference internal" href="exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate">AttributeError</code></a>. This is because the interpreter
will often implicitly request these methods, and gets very confused to
get a new Mock object when it expects a magic method. If you need magic
method support see <a class="reference internal" href="#magic-methods">magic methods</a>.</td></tr>
</tbody>
</table>
</div>
</div>
<div class="section" id="the-patchers">
<h2>26.5.3. The patchers<a class="headerlink" href="#the-patchers" title="Permalink to this headline">¶</a></h2>
The patch decorators are used for patching objects only within the scope of
the function they decorate. They automatically handle the unpatching for you,
even if exceptions are raised. All of these functions can also be used in with
statements or as class decorators.
<div class="section" id="patch">
<h3>26.5.3.1. patch<a class="headerlink" href="#patch" title="Permalink to this headline">¶</a></h3>
<div class="admonition note">
Note
<a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> is straightforward to use. The key is to do the patching in the
right namespace. See the section <a class="reference internal" href="#id5">where to patch</a>.
</div>
<dl class="function">
<dt id="unittest.mock.patch">
<code class="descclassname">unittest.mock.</code><code class="descname">patch</code>(target, new=DEFAULT, spec=None, create=False, spec_set=None, autospec=None, new_callable=None, **kwargs)<a class="headerlink" href="#unittest.mock.patch" title="Permalink to this definition">¶</a></dt>
<dd><a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> acts as a function decorator, class decorator or a context
manager. Inside the body of the function or with statement, the target
is patched with a new object. When the function/with statement exits
the patch is undone.
If new is omitted, then the target is replaced with a
<a class="reference internal" href="#unittest.mock.MagicMock" title="unittest.mock.MagicMock"><code class="xref py py-class docutils literal notranslate">MagicMock</code></a>. If <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> is used as a decorator and new is
omitted, the created mock is passed in as an extra argument to the
decorated function. If <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> is used as a context manager the created
mock is returned by the context manager.
target should be a string in the form <code class="docutils literal notranslate">'package.module.ClassName'</code>. The
target is imported and the specified object replaced with the new
object, so the target must be importable from the environment you are
calling <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> from. The target is imported when the decorated function
is executed, not at decoration time.
The spec and spec_set keyword arguments are passed to the <a class="reference internal" href="#unittest.mock.MagicMock" title="unittest.mock.MagicMock"><code class="xref py py-class docutils literal notranslate">MagicMock</code></a>
if patch is creating one for you.
In addition you can pass <code class="docutils literal notranslate">spec=True</code> or <code class="docutils literal notranslate">spec_set=True</code>, which causes
patch to pass in the object being mocked as the spec/spec_set object.
new_callable allows you to specify a different class, or callable object,
that will be called to create the new object. By default <a class="reference internal" href="#unittest.mock.MagicMock" title="unittest.mock.MagicMock"><code class="xref py py-class docutils literal notranslate">MagicMock</code></a> is
used.
A more powerful form of spec is autospec. If you set <code class="docutils literal notranslate">autospec=True</code>
then the mock will be created with a spec from the object being replaced.
All attributes of the mock will also have the spec of the corresponding
attribute of the object being replaced. Methods and functions being mocked
will have their arguments checked and will raise a <a class="reference internal" href="exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate">TypeError</code></a> if they are
called with the wrong signature. For mocks
replacing a class, their return value (the ‘instance’) will have the same
spec as the class. See the <a class="reference internal" href="#unittest.mock.create_autospec" title="unittest.mock.create_autospec"><code class="xref py py-func docutils literal notranslate">create_autospec()</code></a> function and
<a class="reference internal" href="#auto-speccing">Autospeccing</a>.
Instead of <code class="docutils literal notranslate">autospec=True</code> you can pass <code class="docutils literal notranslate">autospec=some_object</code> to use an
arbitrary object as the spec instead of the one being replaced.
By default <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> will fail to replace attributes that don’t exist. If
you pass in <code class="docutils literal notranslate">create=True</code>, and the attribute doesn’t exist, patch will
create the attribute for you when the patched function is called, and
delete it again afterwards. This is useful for writing tests against
attributes that your production code creates at runtime. It is off by
default because it can be dangerous. With it switched on you can write
passing tests against APIs that don’t actually exist!
<div class="admonition note">
Note
<div class="last versionchanged">
Changed in version 3.5: If you are patching builtins in a module then you don’t
need to pass <code class="docutils literal notranslate">create=True</code>, it will be added by default.
</div>
</div>
Patch can be used as a <code class="xref py py-class docutils literal notranslate">TestCase</code> class decorator. It works by
decorating each test method in the class. This reduces the boilerplate
code when your test methods share a common patchings set. <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> finds
tests by looking for method names that start with <code class="docutils literal notranslate">patch.TEST_PREFIX</code>.
By default this is <code class="docutils literal notranslate">'test'</code>, which matches the way <a class="reference internal" href="unittest.html#module-unittest" title="unittest: Unit testing framework for Python."><code class="xref py py-mod docutils literal notranslate">unittest</code></a> finds tests.
You can specify an alternative prefix by setting <code class="docutils literal notranslate">patch.TEST_PREFIX</code>.
Patch can be used as a context manager, with the with statement. Here the
patching applies to the indented block after the with statement. If you
use “as” then the patched object will be bound to the name after the
“as”; very useful if <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> is creating a mock object for you.
<a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> takes arbitrary keyword arguments. These will be passed to
the <a class="reference internal" href="#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate">Mock</code></a> (or new_callable) on construction.
<code class="docutils literal notranslate">patch.dict(...)</code>, <code class="docutils literal notranslate">patch.multiple(...)</code> and <code class="docutils literal notranslate">patch.object(...)</code> are
available for alternate use-cases.
</dd></dl>

<a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> as function decorator, creating the mock for you and passing it into
the decorated function:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; @patch(&#39;__main__.SomeClass&#39;)
... def function(normal_argument, mock_class):
... print(mock_class is SomeClass)
...
&gt;&gt;&gt; function(None)
True
</pre></div>
</div>
Patching a class replaces the class with a <a class="reference internal" href="#unittest.mock.MagicMock" title="unittest.mock.MagicMock"><code class="xref py py-class docutils literal notranslate">MagicMock</code></a> instance. If the
class is instantiated in the code under test then it will be the
<a class="reference internal" href="#unittest.mock.Mock.return_value" title="unittest.mock.Mock.return_value"><code class="xref py py-attr docutils literal notranslate">return_value</code></a> of the mock that will be used.
If the class is instantiated multiple times you could use
<a class="reference internal" href="#unittest.mock.Mock.side_effect" title="unittest.mock.Mock.side_effect"><code class="xref py py-attr docutils literal notranslate">side_effect</code></a> to return a new mock each time. Alternatively you
can set the return_value to be anything you want.
To configure return values on methods of instances on the patched class
you must do this on the <code class="xref py py-attr docutils literal notranslate">return_value</code>. For example:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class Class:
... def method(self):
... pass
...
&gt;&gt;&gt; with patch(&#39;__main__.Class&#39;) as MockClass:
... instance = MockClass.return_value
... instance.method.return_value = &#39;foo&#39;
... assert Class() is instance
... assert Class().method() == &#39;foo&#39;
...
</pre></div>
</div>
If you use spec or spec_set and <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> is replacing a class, then the
return value of the created mock will have the same spec.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; Original = Class
&gt;&gt;&gt; patcher = patch(&#39;__main__.Class&#39;, spec=True)
&gt;&gt;&gt; MockClass = patcher.start()
&gt;&gt;&gt; instance = MockClass()
&gt;&gt;&gt; assert isinstance(instance, Original)
&gt;&gt;&gt; patcher.stop()
</pre></div>
</div>
The new_callable argument is useful where you want to use an alternative
class to the default <a class="reference internal" href="#unittest.mock.MagicMock" title="unittest.mock.MagicMock"><code class="xref py py-class docutils literal notranslate">MagicMock</code></a> for the created mock. For example, if
you wanted a <a class="reference internal" href="#unittest.mock.NonCallableMock" title="unittest.mock.NonCallableMock"><code class="xref py py-class docutils literal notranslate">NonCallableMock</code></a> to be used:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; thing = object()
&gt;&gt;&gt; with patch(&#39;__main__.thing&#39;, new_callable=NonCallableMock) as mock_thing:
... assert thing is mock_thing
... thing()
...
Traceback (most recent call last):
 ...
TypeError: &#39;NonCallableMock&#39; object is not callable
</pre></div>
</div>
Another use case might be to replace an object with an <a class="reference internal" href="io.html#io.StringIO" title="io.StringIO"><code class="xref py py-class docutils literal notranslate">io.StringIO</code></a> instance:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; from io import StringIO
&gt;&gt;&gt; def foo():
... print(&#39;Something&#39;)
...
&gt;&gt;&gt; @patch(&#39;sys.stdout&#39;, new_callable=StringIO)
... def test(mock_stdout):
... foo()
... assert mock_stdout.getvalue() == &#39;Something\n&#39;
...
&gt;&gt;&gt; test()
</pre></div>
</div>
When <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> is creating a mock for you, it is common that the first thing
you need to do is to configure the mock. Some of that configuration can be done
in the call to patch. Any arbitrary keywords you pass into the call will be
used to set attributes on the created mock:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; patcher = patch(&#39;__main__.thing&#39;, first=&#39;one&#39;, second=&#39;two&#39;)
&gt;&gt;&gt; mock_thing = patcher.start()
&gt;&gt;&gt; mock_thing.first
&#39;one&#39;
&gt;&gt;&gt; mock_thing.second
&#39;two&#39;
</pre></div>
</div>
As well as attributes on the created mock attributes, like the
<a class="reference internal" href="#unittest.mock.Mock.return_value" title="unittest.mock.Mock.return_value"><code class="xref py py-attr docutils literal notranslate">return_value</code></a> and <a class="reference internal" href="#unittest.mock.Mock.side_effect" title="unittest.mock.Mock.side_effect"><code class="xref py py-attr docutils literal notranslate">side_effect</code></a>, of child mocks can
also be configured. These aren’t syntactically valid to pass in directly as
keyword arguments, but a dictionary with these as keys can still be expanded
into a <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> call using <code class="docutils literal notranslate">**</code>:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; config = {&#39;method.return_value&#39;: 3, &#39;other.side_effect&#39;: KeyError}
&gt;&gt;&gt; patcher = patch(&#39;__main__.thing&#39;, **config)
&gt;&gt;&gt; mock_thing = patcher.start()
&gt;&gt;&gt; mock_thing.method()
3
&gt;&gt;&gt; mock_thing.other()
Traceback (most recent call last):
 ...
KeyError
</pre></div>
</div>
</div>
<div class="section" id="patch-object">
<h3>26.5.3.2. patch.object<a class="headerlink" href="#patch-object" title="Permalink to this headline">¶</a></h3>
<dl class="function">
<dt id="unittest.mock.patch.object">
<code class="descclassname">patch.</code><code class="descname">object</code>(target, attribute, new=DEFAULT, spec=None, create=False, spec_set=None, autospec=None, new_callable=None, **kwargs)<a class="headerlink" href="#unittest.mock.patch.object" title="Permalink to this definition">¶</a></dt>
<dd>patch the named member (attribute) on an object (target) with a mock
object.
<a class="reference internal" href="#unittest.mock.patch.object" title="unittest.mock.patch.object"><code class="xref py py-func docutils literal notranslate">patch.object()</code></a> can be used as a decorator, class decorator or a context
manager. Arguments new, spec, create, spec_set, autospec and
new_callable have the same meaning as for <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a>. Like <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a>,
<a class="reference internal" href="#unittest.mock.patch.object" title="unittest.mock.patch.object"><code class="xref py py-func docutils literal notranslate">patch.object()</code></a> takes arbitrary keyword arguments for configuring the mock
object it creates.
When used as a class decorator <a class="reference internal" href="#unittest.mock.patch.object" title="unittest.mock.patch.object"><code class="xref py py-func docutils literal notranslate">patch.object()</code></a> honours <code class="docutils literal notranslate">patch.TEST_PREFIX</code>
for choosing which methods to wrap.
</dd></dl>

You can either call <a class="reference internal" href="#unittest.mock.patch.object" title="unittest.mock.patch.object"><code class="xref py py-func docutils literal notranslate">patch.object()</code></a> with three arguments or two arguments. The
three argument form takes the object to be patched, the attribute name and the
object to replace the attribute with.
When calling with the two argument form you omit the replacement object, and a
mock is created for you and passed in as an extra argument to the decorated
function:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; @patch.object(SomeClass, &#39;class_method&#39;)
... def test(mock_method):
... SomeClass.class_method(3)
... mock_method.assert_called_with(3)
...
&gt;&gt;&gt; test()
</pre></div>
</div>
spec, create and the other arguments to <a class="reference internal" href="#unittest.mock.patch.object" title="unittest.mock.patch.object"><code class="xref py py-func docutils literal notranslate">patch.object()</code></a> have the same
meaning as they do for <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a>.
</div>
<div class="section" id="patch-dict">
<h3>26.5.3.3. patch.dict<a class="headerlink" href="#patch-dict" title="Permalink to this headline">¶</a></h3>
<dl class="function">
<dt id="unittest.mock.patch.dict">
<code class="descclassname">patch.</code><code class="descname">dict</code>(in_dict, values=(), clear=False, **kwargs)<a class="headerlink" href="#unittest.mock.patch.dict" title="Permalink to this definition">¶</a></dt>
<dd>Patch a dictionary, or dictionary like object, and restore the dictionary
to its original state after the test.
in_dict can be a dictionary or a mapping like container. If it is a
mapping then it must at least support getting, setting and deleting items
plus iterating over keys.
in_dict can also be a string specifying the name of the dictionary, which
will then be fetched by importing it.
values can be a dictionary of values to set in the dictionary. values
can also be an iterable of <code class="docutils literal notranslate">(key, value)</code> pairs.
If clear is true then the dictionary will be cleared before the new
values are set.
<a class="reference internal" href="#unittest.mock.patch.dict" title="unittest.mock.patch.dict"><code class="xref py py-func docutils literal notranslate">patch.dict()</code></a> can also be called with arbitrary keyword arguments to set
values in the dictionary.
<a class="reference internal" href="#unittest.mock.patch.dict" title="unittest.mock.patch.dict"><code class="xref py py-func docutils literal notranslate">patch.dict()</code></a> can be used as a context manager, decorator or class
decorator. When used as a class decorator <a class="reference internal" href="#unittest.mock.patch.dict" title="unittest.mock.patch.dict"><code class="xref py py-func docutils literal notranslate">patch.dict()</code></a> honours
<code class="docutils literal notranslate">patch.TEST_PREFIX</code> for choosing which methods to wrap.
</dd></dl>

<a class="reference internal" href="#unittest.mock.patch.dict" title="unittest.mock.patch.dict"><code class="xref py py-func docutils literal notranslate">patch.dict()</code></a> can be used to add members to a dictionary, or simply let a test
change a dictionary, and ensure the dictionary is restored when the test
ends.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; foo = {}
&gt;&gt;&gt; with patch.dict(foo, {&#39;newkey&#39;: &#39;newvalue&#39;}):
... assert foo == {&#39;newkey&#39;: &#39;newvalue&#39;}
...
&gt;&gt;&gt; assert foo == {}
</pre></div>
</div>
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; import os
&gt;&gt;&gt; with patch.dict(&#39;os.environ&#39;, {&#39;newkey&#39;: &#39;newvalue&#39;}):
... print(os.environ[&#39;newkey&#39;])
...
newvalue
&gt;&gt;&gt; assert &#39;newkey&#39; not in os.environ
</pre></div>
</div>
Keywords can be used in the <a class="reference internal" href="#unittest.mock.patch.dict" title="unittest.mock.patch.dict"><code class="xref py py-func docutils literal notranslate">patch.dict()</code></a> call to set values in the dictionary:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mymodule = MagicMock()
&gt;&gt;&gt; mymodule.function.return_value = &#39;fish&#39;
&gt;&gt;&gt; with patch.dict(&#39;sys.modules&#39;, mymodule=mymodule):
... import mymodule
... mymodule.function(&#39;some&#39;, &#39;args&#39;)
...
&#39;fish&#39;
</pre></div>
</div>
<a class="reference internal" href="#unittest.mock.patch.dict" title="unittest.mock.patch.dict"><code class="xref py py-func docutils literal notranslate">patch.dict()</code></a> can be used with dictionary like objects that aren’t actually
dictionaries. At the very minimum they must support item getting, setting,
deleting and either iteration or membership test. This corresponds to the
magic methods <a class="reference internal" href="../reference/datamodel.html#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate">__getitem__()</code></a>, <a class="reference internal" href="../reference/datamodel.html#object.__setitem__" title="object.__setitem__"><code class="xref py py-meth docutils literal notranslate">__setitem__()</code></a>, <a class="reference internal" href="../reference/datamodel.html#object.__delitem__" title="object.__delitem__"><code class="xref py py-meth docutils literal notranslate">__delitem__()</code></a> and either
<a class="reference internal" href="../reference/datamodel.html#object.__iter__" title="object.__iter__"><code class="xref py py-meth docutils literal notranslate">__iter__()</code></a> or <a class="reference internal" href="../reference/datamodel.html#object.__contains__" title="object.__contains__"><code class="xref py py-meth docutils literal notranslate">__contains__()</code></a>.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class Container:
... def __init__(self):
... self.values = {}
... def __getitem__(self, name):
... return self.values[name]
... def __setitem__(self, name, value):
... self.values[name] = value
... def __delitem__(self, name):
... del self.values[name]
... def __iter__(self):
... return iter(self.values)
...
&gt;&gt;&gt; thing = Container()
&gt;&gt;&gt; thing[&#39;one&#39;] = 1
&gt;&gt;&gt; with patch.dict(thing, one=2, two=3):
... assert thing[&#39;one&#39;] == 2
... assert thing[&#39;two&#39;] == 3
...
&gt;&gt;&gt; assert thing[&#39;one&#39;] == 1
&gt;&gt;&gt; assert list(thing) == [&#39;one&#39;]
</pre></div>
</div>
</div>
<div class="section" id="patch-multiple">
<h3>26.5.3.4. patch.multiple<a class="headerlink" href="#patch-multiple" title="Permalink to this headline">¶</a></h3>
<dl class="function">
<dt id="unittest.mock.patch.multiple">
<code class="descclassname">patch.</code><code class="descname">multiple</code>(target, spec=None, create=False, spec_set=None, autospec=None, new_callable=None, **kwargs)<a class="headerlink" href="#unittest.mock.patch.multiple" title="Permalink to this definition">¶</a></dt>
<dd>Perform multiple patches in a single call. It takes the object to be
patched (either as an object or a string to fetch the object by importing)
and keyword arguments for the patches:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>with patch.multiple(settings, FIRST_PATCH=&#39;one&#39;, SECOND_PATCH=&#39;two&#39;):
 ...
</pre></div>
</div>
Use <a class="reference internal" href="#unittest.mock.DEFAULT" title="unittest.mock.DEFAULT"><code class="xref py py-data docutils literal notranslate">DEFAULT</code></a> as the value if you want <a class="reference internal" href="#unittest.mock.patch.multiple" title="unittest.mock.patch.multiple"><code class="xref py py-func docutils literal notranslate">patch.multiple()</code></a> to create
mocks for you. In this case the created mocks are passed into a decorated
function by keyword, and a dictionary is returned when <a class="reference internal" href="#unittest.mock.patch.multiple" title="unittest.mock.patch.multiple"><code class="xref py py-func docutils literal notranslate">patch.multiple()</code></a> is
used as a context manager.
<a class="reference internal" href="#unittest.mock.patch.multiple" title="unittest.mock.patch.multiple"><code class="xref py py-func docutils literal notranslate">patch.multiple()</code></a> can be used as a decorator, class decorator or a context
manager. The arguments spec, spec_set, create, autospec and
new_callable have the same meaning as for <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a>. These arguments will
be applied to all patches done by <a class="reference internal" href="#unittest.mock.patch.multiple" title="unittest.mock.patch.multiple"><code class="xref py py-func docutils literal notranslate">patch.multiple()</code></a>.
When used as a class decorator <a class="reference internal" href="#unittest.mock.patch.multiple" title="unittest.mock.patch.multiple"><code class="xref py py-func docutils literal notranslate">patch.multiple()</code></a> honours <code class="docutils literal notranslate">patch.TEST_PREFIX</code>
for choosing which methods to wrap.
</dd></dl>

If you want <a class="reference internal" href="#unittest.mock.patch.multiple" title="unittest.mock.patch.multiple"><code class="xref py py-func docutils literal notranslate">patch.multiple()</code></a> to create mocks for you, then you can use
<a class="reference internal" href="#unittest.mock.DEFAULT" title="unittest.mock.DEFAULT"><code class="xref py py-data docutils literal notranslate">DEFAULT</code></a> as the value. If you use <a class="reference internal" href="#unittest.mock.patch.multiple" title="unittest.mock.patch.multiple"><code class="xref py py-func docutils literal notranslate">patch.multiple()</code></a> as a decorator
then the created mocks are passed into the decorated function by keyword.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; thing = object()
&gt;&gt;&gt; other = object()
</pre></div>
</div>
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; @patch.multiple(&#39;__main__&#39;, thing=DEFAULT, other=DEFAULT)
... def test_function(thing, other):
... assert isinstance(thing, MagicMock)
... assert isinstance(other, MagicMock)
...
&gt;&gt;&gt; test_function()
</pre></div>
</div>
<a class="reference internal" href="#unittest.mock.patch.multiple" title="unittest.mock.patch.multiple"><code class="xref py py-func docutils literal notranslate">patch.multiple()</code></a> can be nested with other <code class="docutils literal notranslate">patch</code> decorators, but put arguments
passed by keyword after any of the standard arguments created by <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a>:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; @patch(&#39;sys.exit&#39;)
... @patch.multiple(&#39;__main__&#39;, thing=DEFAULT, other=DEFAULT)
... def test_function(mock_exit, other, thing):
... assert &#39;other&#39; in repr(other)
... assert &#39;thing&#39; in repr(thing)
... assert &#39;exit&#39; in repr(mock_exit)
...
&gt;&gt;&gt; test_function()
</pre></div>
</div>
If <a class="reference internal" href="#unittest.mock.patch.multiple" title="unittest.mock.patch.multiple"><code class="xref py py-func docutils literal notranslate">patch.multiple()</code></a> is used as a context manager, the value returned by the
context manger is a dictionary where created mocks are keyed by name:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; with patch.multiple(&#39;__main__&#39;, thing=DEFAULT, other=DEFAULT) as values:
... assert &#39;other&#39; in repr(values[&#39;other&#39;])
... assert &#39;thing&#39; in repr(values[&#39;thing&#39;])
... assert values[&#39;thing&#39;] is thing
... assert values[&#39;other&#39;] is other
...
</pre></div>
</div>
</div>
<div class="section" id="patch-methods-start-and-stop">
<h3>26.5.3.5. patch methods: start and stop<a class="headerlink" href="#patch-methods-start-and-stop" title="Permalink to this headline">¶</a></h3>
All the patchers have <code class="xref py py-meth docutils literal notranslate">start()</code> and <code class="xref py py-meth docutils literal notranslate">stop()</code> methods. These make it simpler to do
patching in <code class="docutils literal notranslate">setUp</code> methods or where you want to do multiple patches without
nesting decorators or with statements.
To use them call <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a>, <a class="reference internal" href="#unittest.mock.patch.object" title="unittest.mock.patch.object"><code class="xref py py-func docutils literal notranslate">patch.object()</code></a> or <a class="reference internal" href="#unittest.mock.patch.dict" title="unittest.mock.patch.dict"><code class="xref py py-func docutils literal notranslate">patch.dict()</code></a> as
normal and keep a reference to the returned <code class="docutils literal notranslate">patcher</code> object. You can then
call <code class="xref py py-meth docutils literal notranslate">start()</code> to put the patch in place and <code class="xref py py-meth docutils literal notranslate">stop()</code> to undo it.
If you are using <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> to create a mock for you then it will be returned by
the call to <code class="docutils literal notranslate">patcher.start</code>.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; patcher = patch(&#39;package.module.ClassName&#39;)
&gt;&gt;&gt; from package import module
&gt;&gt;&gt; original = module.ClassName
&gt;&gt;&gt; new_mock = patcher.start()
&gt;&gt;&gt; assert module.ClassName is not original
&gt;&gt;&gt; assert module.ClassName is new_mock
&gt;&gt;&gt; patcher.stop()
&gt;&gt;&gt; assert module.ClassName is original
&gt;&gt;&gt; assert module.ClassName is not new_mock
</pre></div>
</div>
A typical use case for this might be for doing multiple patches in the <code class="docutils literal notranslate">setUp</code>
method of a <code class="xref py py-class docutils literal notranslate">TestCase</code>:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class MyTest(TestCase):
... def setUp(self):
... self.patcher1 = patch(&#39;package.module.Class1&#39;)
... self.patcher2 = patch(&#39;package.module.Class2&#39;)
... self.MockClass1 = self.patcher1.start()
... self.MockClass2 = self.patcher2.start()
...
... def tearDown(self):
... self.patcher1.stop()
... self.patcher2.stop()
...
... def test_something(self):
... assert package.module.Class1 is self.MockClass1
... assert package.module.Class2 is self.MockClass2
...
&gt;&gt;&gt; MyTest(&#39;test_something&#39;).run()
</pre></div>
</div>
<div class="admonition caution">
Caution
If you use this technique you must ensure that the patching is “undone” by
calling <code class="docutils literal notranslate">stop</code>. This can be fiddlier than you might think, because if an
exception is raised in the <code class="docutils literal notranslate">setUp</code> then <code class="docutils literal notranslate">tearDown</code> is not called.
<a class="reference internal" href="unittest.html#unittest.TestCase.addCleanup" title="unittest.TestCase.addCleanup"><code class="xref py py-meth docutils literal notranslate">unittest.TestCase.addCleanup()</code></a> makes this easier:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class MyTest(TestCase):
... def setUp(self):
... patcher = patch(&#39;package.module.Class&#39;)
... self.MockClass = patcher.start()
... self.addCleanup(patcher.stop)
...
... def test_something(self):
... assert package.module.Class is self.MockClass
...
</pre></div>
</div>
As an added bonus you no longer need to keep a reference to the <code class="docutils literal notranslate">patcher</code>
object.
</div>
It is also possible to stop all patches which have been started by using
<a class="reference internal" href="#unittest.mock.patch.stopall" title="unittest.mock.patch.stopall"><code class="xref py py-func docutils literal notranslate">patch.stopall()</code></a>.
<dl class="function">
<dt id="unittest.mock.patch.stopall">
<code class="descclassname">patch.</code><code class="descname">stopall</code>()<a class="headerlink" href="#unittest.mock.patch.stopall" title="Permalink to this definition">¶</a></dt>
<dd>Stop all active patches. Only stops patches started with <code class="docutils literal notranslate">start</code>.
</dd></dl>

</div>
<div class="section" id="patch-builtins">
<h3>26.5.3.6. patch builtins<a class="headerlink" href="#patch-builtins" title="Permalink to this headline">¶</a></h3>
You can patch any builtins within a module. The following example patches
builtin <a class="reference internal" href="functions.html#ord" title="ord"><code class="xref py py-func docutils literal notranslate">ord()</code></a>:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; @patch(&#39;__main__.ord&#39;)
... def test(mock_ord):
... mock_ord.return_value = 101
... print(ord(&#39;c&#39;))
...
&gt;&gt;&gt; test()
101
</pre></div>
</div>
</div>
<div class="section" id="test-prefix">
<h3>26.5.3.7. TEST_PREFIX<a class="headerlink" href="#test-prefix" title="Permalink to this headline">¶</a></h3>
All of the patchers can be used as class decorators. When used in this way
they wrap every test method on the class. The patchers recognise methods that
start with <code class="docutils literal notranslate">'test'</code> as being test methods. This is the same way that the
<a class="reference internal" href="unittest.html#unittest.TestLoader" title="unittest.TestLoader"><code class="xref py py-class docutils literal notranslate">unittest.TestLoader</code></a> finds test methods by default.
It is possible that you want to use a different prefix for your tests. You can
inform the patchers of the different prefix by setting <code class="docutils literal notranslate">patch.TEST_PREFIX</code>:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; patch.TEST_PREFIX = &#39;foo&#39;
&gt;&gt;&gt; value = 3
&gt;&gt;&gt;
&gt;&gt;&gt; @patch(&#39;__main__.value&#39;, &#39;not three&#39;)
... class Thing:
... def foo_one(self):
... print(value)
... def foo_two(self):
... print(value)
...
&gt;&gt;&gt;
&gt;&gt;&gt; Thing().foo_one()
not three
&gt;&gt;&gt; Thing().foo_two()
not three
&gt;&gt;&gt; value
3
</pre></div>
</div>
</div>
<div class="section" id="nesting-patch-decorators">
<h3>26.5.3.8. Nesting Patch Decorators<a class="headerlink" href="#nesting-patch-decorators" title="Permalink to this headline">¶</a></h3>
If you want to perform multiple patches then you can simply stack up the
decorators.
You can stack up multiple patch decorators using this pattern:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; @patch.object(SomeClass, &#39;class_method&#39;)
... @patch.object(SomeClass, &#39;static_method&#39;)
... def test(mock1, mock2):
... assert SomeClass.static_method is mock1
... assert SomeClass.class_method is mock2
... SomeClass.static_method(&#39;foo&#39;)
... SomeClass.class_method(&#39;bar&#39;)
... return mock1, mock2
...
&gt;&gt;&gt; mock1, mock2 = test()
&gt;&gt;&gt; mock1.assert_called_once_with(&#39;foo&#39;)
&gt;&gt;&gt; mock2.assert_called_once_with(&#39;bar&#39;)
</pre></div>
</div>
Note that the decorators are applied from the bottom upwards. This is the
standard way that Python applies decorators. The order of the created mocks
passed into your test function matches this order.
</div>
<div class="section" id="where-to-patch">
<h3>26.5.3.9. Where to patch<a class="headerlink" href="#where-to-patch" title="Permalink to this headline">¶</a></h3>
<a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> works by (temporarily) changing the object that a name points to with
another one. There can be many names pointing to any individual object, so
for patching to work you must ensure that you patch the name used by the system
under test.
The basic principle is that you patch where an object is looked up, which
is not necessarily the same place as where it is defined. A couple of
examples will help to clarify this.
Imagine we have a project that we want to test with the following structure:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>a.py
 -&gt; Defines SomeClass

b.py
 -&gt; from a import SomeClass
 -&gt; some_function instantiates SomeClass
</pre></div>
</div>
Now we want to test <code class="docutils literal notranslate">some_function</code> but we want to mock out <code class="docutils literal notranslate">SomeClass</code> using
<a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a>. The problem is that when we import module b, which we will have to
do then it imports <code class="docutils literal notranslate">SomeClass</code> from module a. If we use <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> to mock out
<code class="docutils literal notranslate">a.SomeClass</code> then it will have no effect on our test; module b already has a
reference to the real <code class="docutils literal notranslate">SomeClass</code> and it looks like our patching had no
effect.
The key is to patch out <code class="docutils literal notranslate">SomeClass</code> where it is used (or where it is looked up
). In this case <code class="docutils literal notranslate">some_function</code> will actually look up <code class="docutils literal notranslate">SomeClass</code> in module b,
where we have imported it. The patching should look like:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>@patch(&#39;b.SomeClass&#39;)
</pre></div>
</div>
However, consider the alternative scenario where instead of <code class="docutils literal notranslate">from a import
SomeClass</code> module b does <code class="docutils literal notranslate">import a</code> and <code class="docutils literal notranslate">some_function</code> uses <code class="docutils literal notranslate">a.SomeClass</code>. Both
of these import forms are common. In this case the class we want to patch is
being looked up in the module and so we have to patch <code class="docutils literal notranslate">a.SomeClass</code> instead:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>@patch(&#39;a.SomeClass&#39;)
</pre></div>
</div>
</div>
<div class="section" id="patching-descriptors-and-proxy-objects">
<h3>26.5.3.10. Patching Descriptors and Proxy Objects<a class="headerlink" href="#patching-descriptors-and-proxy-objects" title="Permalink to this headline">¶</a></h3>
Both <a class="reference internal" href="#patch">patch</a> and <a class="reference internal" href="#patch-object">patch.object</a> correctly patch and restore descriptors: class
methods, static methods and properties. You should patch these on the class
rather than an instance. They also work with some objects
that proxy attribute access, like the <a class="reference external" href="http://www.voidspace.org.uk/python/weblog/arch_d7_2010_12_04.shtml#e1198">django settings object</a>.
</div>
</div>
<div class="section" id="magicmock-and-magic-method-support">
<h2>26.5.4. MagicMock and magic method support<a class="headerlink" href="#magicmock-and-magic-method-support" title="Permalink to this headline">¶</a></h2>
<div class="section" id="mocking-magic-methods">
<h3>26.5.4.1. Mocking Magic Methods<a class="headerlink" href="#mocking-magic-methods" title="Permalink to this headline">¶</a></h3>
<a class="reference internal" href="#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate">Mock</code></a> supports mocking the Python protocol methods, also known as
“magic methods”. This allows mock objects to replace containers or other
objects that implement Python protocols.
Because magic methods are looked up differently from normal methods <a class="footnote-reference" href="#id8" id="id6">[2]</a>, this
support has been specially implemented. This means that only specific magic
methods are supported. The supported list includes almost all of them. If
there are any missing that you need please let us know.
You mock magic methods by setting the method you are interested in to a function
or a mock instance. If you are using a function then it must take <code class="docutils literal notranslate">self</code> as
the first argument <a class="footnote-reference" href="#id9" id="id7">[3]</a>.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; def __str__(self):
... return &#39;fooble&#39;
...
&gt;&gt;&gt; mock = Mock()
&gt;&gt;&gt; mock.__str__ = __str__
&gt;&gt;&gt; str(mock)
&#39;fooble&#39;
</pre></div>
</div>
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock()
&gt;&gt;&gt; mock.__str__ = Mock()
&gt;&gt;&gt; mock.__str__.return_value = &#39;fooble&#39;
&gt;&gt;&gt; str(mock)
&#39;fooble&#39;
</pre></div>
</div>
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock()
&gt;&gt;&gt; mock.__iter__ = Mock(return_value=iter([]))
&gt;&gt;&gt; list(mock)
[]
</pre></div>
</div>
One use case for this is for mocking objects used as context managers in a
<a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal notranslate">with</code></a> statement:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock()
&gt;&gt;&gt; mock.__enter__ = Mock(return_value=&#39;foo&#39;)
&gt;&gt;&gt; mock.__exit__ = Mock(return_value=False)
&gt;&gt;&gt; with mock as m:
... assert m == &#39;foo&#39;
...
&gt;&gt;&gt; mock.__enter__.assert_called_with()
&gt;&gt;&gt; mock.__exit__.assert_called_with(None, None, None)
</pre></div>
</div>
Calls to magic methods do not appear in <a class="reference internal" href="#unittest.mock.Mock.method_calls" title="unittest.mock.Mock.method_calls"><code class="xref py py-attr docutils literal notranslate">method_calls</code></a>, but they
are recorded in <a class="reference internal" href="#unittest.mock.Mock.mock_calls" title="unittest.mock.Mock.mock_calls"><code class="xref py py-attr docutils literal notranslate">mock_calls</code></a>.
<div class="admonition note">
Note
If you use the spec keyword argument to create a mock then attempting to
set a magic method that isn’t in the spec will raise an <a class="reference internal" href="exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate">AttributeError</code></a>.
</div>
The full list of supported magic methods is:
<ul class="simple">
<li><code class="docutils literal notranslate">__hash__</code>, <code class="docutils literal notranslate">__sizeof__</code>, <code class="docutils literal notranslate">__repr__</code> and <code class="docutils literal notranslate">__str__</code></li>
<li><code class="docutils literal notranslate">__dir__</code>, <code class="docutils literal notranslate">__format__</code> and <code class="docutils literal notranslate">__subclasses__</code></li>
<li><code class="docutils literal notranslate">__floor__</code>, <code class="docutils literal notranslate">__trunc__</code> and <code class="docutils literal notranslate">__ceil__</code></li>
<li>Comparisons: <code class="docutils literal notranslate">__lt__</code>, <code class="docutils literal notranslate">__gt__</code>, <code class="docutils literal notranslate">__le__</code>, <code class="docutils literal notranslate">__ge__</code>,
<code class="docutils literal notranslate">__eq__</code> and <code class="docutils literal notranslate">__ne__</code></li>
<li>Container methods: <code class="docutils literal notranslate">__getitem__</code>, <code class="docutils literal notranslate">__setitem__</code>, <code class="docutils literal notranslate">__delitem__</code>,
<code class="docutils literal notranslate">__contains__</code>, <code class="docutils literal notranslate">__len__</code>, <code class="docutils literal notranslate">__iter__</code>, <code class="docutils literal notranslate">__reversed__</code>
and <code class="docutils literal notranslate">__missing__</code></li>
<li>Context manager: <code class="docutils literal notranslate">__enter__</code> and <code class="docutils literal notranslate">__exit__</code></li>
<li>Unary numeric methods: <code class="docutils literal notranslate">__neg__</code>, <code class="docutils literal notranslate">__pos__</code> and <code class="docutils literal notranslate">__invert__</code></li>
<li>The numeric methods (including right hand and in-place variants):
<code class="docutils literal notranslate">__add__</code>, <code class="docutils literal notranslate">__sub__</code>, <code class="docutils literal notranslate">__mul__</code>, <code class="docutils literal notranslate">__matmul__</code>, <code class="docutils literal notranslate">__div__</code>, <code class="docutils literal notranslate">__truediv__</code>,
<code class="docutils literal notranslate">__floordiv__</code>, <code class="docutils literal notranslate">__mod__</code>, <code class="docutils literal notranslate">__divmod__</code>, <code class="docutils literal notranslate">__lshift__</code>,
<code class="docutils literal notranslate">__rshift__</code>, <code class="docutils literal notranslate">__and__</code>, <code class="docutils literal notranslate">__xor__</code>, <code class="docutils literal notranslate">__or__</code>, and <code class="docutils literal notranslate">__pow__</code></li>
<li>Numeric conversion methods: <code class="docutils literal notranslate">__complex__</code>, <code class="docutils literal notranslate">__int__</code>, <code class="docutils literal notranslate">__float__</code>
and <code class="docutils literal notranslate">__index__</code></li>
<li>Descriptor methods: <code class="docutils literal notranslate">__get__</code>, <code class="docutils literal notranslate">__set__</code> and <code class="docutils literal notranslate">__delete__</code></li>
<li>Pickling: <code class="docutils literal notranslate">__reduce__</code>, <code class="docutils literal notranslate">__reduce_ex__</code>, <code class="docutils literal notranslate">__getinitargs__</code>,
<code class="docutils literal notranslate">__getnewargs__</code>, <code class="docutils literal notranslate">__getstate__</code> and <code class="docutils literal notranslate">__setstate__</code></li>
</ul>
The following methods exist but are not supported as they are either in use
by mock, can’t be set dynamically, or can cause problems:
<ul class="simple">
<li><code class="docutils literal notranslate">__getattr__</code>, <code class="docutils literal notranslate">__setattr__</code>, <code class="docutils literal notranslate">__init__</code> and <code class="docutils literal notranslate">__new__</code></li>
<li><code class="docutils literal notranslate">__prepare__</code>, <code class="docutils literal notranslate">__instancecheck__</code>, <code class="docutils literal notranslate">__subclasscheck__</code>, <code class="docutils literal notranslate">__del__</code></li>
</ul>
</div>
<div class="section" id="magic-mock">
<h3>26.5.4.2. Magic Mock<a class="headerlink" href="#magic-mock" title="Permalink to this headline">¶</a></h3>
There are two <code class="docutils literal notranslate">MagicMock</code> variants: <a class="reference internal" href="#unittest.mock.MagicMock" title="unittest.mock.MagicMock"><code class="xref py py-class docutils literal notranslate">MagicMock</code></a> and <a class="reference internal" href="#unittest.mock.NonCallableMagicMock" title="unittest.mock.NonCallableMagicMock"><code class="xref py py-class docutils literal notranslate">NonCallableMagicMock</code></a>.
<dl class="class">
<dt id="unittest.mock.MagicMock">
class <code class="descclassname">unittest.mock.</code><code class="descname">MagicMock</code>(*args, **kw)<a class="headerlink" href="#unittest.mock.MagicMock" title="Permalink to this definition">¶</a></dt>
<dd><code class="docutils literal notranslate">MagicMock</code> is a subclass of <a class="reference internal" href="#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate">Mock</code></a> with default implementations
of most of the magic methods. You can use <code class="docutils literal notranslate">MagicMock</code> without having to
configure the magic methods yourself.
The constructor parameters have the same meaning as for <a class="reference internal" href="#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate">Mock</code></a>.
If you use the spec or spec_set arguments then only magic methods
that exist in the spec will be created.
</dd></dl>

<dl class="class">
<dt id="unittest.mock.NonCallableMagicMock">
class <code class="descclassname">unittest.mock.</code><code class="descname">NonCallableMagicMock</code>(*args, **kw)<a class="headerlink" href="#unittest.mock.NonCallableMagicMock" title="Permalink to this definition">¶</a></dt>
<dd>A non-callable version of <a class="reference internal" href="#unittest.mock.MagicMock" title="unittest.mock.MagicMock"><code class="xref py py-class docutils literal notranslate">MagicMock</code></a>.
The constructor parameters have the same meaning as for
<a class="reference internal" href="#unittest.mock.MagicMock" title="unittest.mock.MagicMock"><code class="xref py py-class docutils literal notranslate">MagicMock</code></a>, with the exception of return_value and
side_effect which have no meaning on a non-callable mock.
</dd></dl>

The magic methods are setup with <a class="reference internal" href="#unittest.mock.MagicMock" title="unittest.mock.MagicMock"><code class="xref py py-class docutils literal notranslate">MagicMock</code></a> objects, so you can configure them
and use them in the usual way:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = MagicMock()
&gt;&gt;&gt; mock[3] = &#39;fish&#39;
&gt;&gt;&gt; mock.__setitem__.assert_called_with(3, &#39;fish&#39;)
&gt;&gt;&gt; mock.__getitem__.return_value = &#39;result&#39;
&gt;&gt;&gt; mock[2]
&#39;result&#39;
</pre></div>
</div>
By default many of the protocol methods are required to return objects of a
specific type. These methods are preconfigured with a default return value, so
that they can be used without you having to do anything if you aren’t interested
in the return value. You can still set the return value manually if you want
to change the default.
Methods and their defaults:
<ul class="simple">
<li><code class="docutils literal notranslate">__lt__</code>: NotImplemented</li>
<li><code class="docutils literal notranslate">__gt__</code>: NotImplemented</li>
<li><code class="docutils literal notranslate">__le__</code>: NotImplemented</li>
<li><code class="docutils literal notranslate">__ge__</code>: NotImplemented</li>
<li><code class="docutils literal notranslate">__int__</code>: 1</li>
<li><code class="docutils literal notranslate">__contains__</code>: False</li>
<li><code class="docutils literal notranslate">__len__</code>: 0</li>
<li><code class="docutils literal notranslate">__iter__</code>: iter([])</li>
<li><code class="docutils literal notranslate">__exit__</code>: False</li>
<li><code class="docutils literal notranslate">__complex__</code>: 1j</li>
<li><code class="docutils literal notranslate">__float__</code>: 1.0</li>
<li><code class="docutils literal notranslate">__bool__</code>: True</li>
<li><code class="docutils literal notranslate">__index__</code>: 1</li>
<li><code class="docutils literal notranslate">__hash__</code>: default hash for the mock</li>
<li><code class="docutils literal notranslate">__str__</code>: default str for the mock</li>
<li><code class="docutils literal notranslate">__sizeof__</code>: default sizeof for the mock</li>
</ul>
For example:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = MagicMock()
&gt;&gt;&gt; int(mock)
1
&gt;&gt;&gt; len(mock)
0
&gt;&gt;&gt; list(mock)
[]
&gt;&gt;&gt; object() in mock
False
</pre></div>
</div>
The two equality methods, <a class="reference internal" href="../reference/datamodel.html#object.__eq__" title="object.__eq__"><code class="xref py py-meth docutils literal notranslate">__eq__()</code></a> and <a class="reference internal" href="../reference/datamodel.html#object.__ne__" title="object.__ne__"><code class="xref py py-meth docutils literal notranslate">__ne__()</code></a>, are special.
They do the default equality comparison on identity, using the
<a class="reference internal" href="#unittest.mock.Mock.side_effect" title="unittest.mock.Mock.side_effect"><code class="xref py py-attr docutils literal notranslate">side_effect</code></a> attribute, unless you change their return value to
return something else:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; MagicMock() == 3
False
&gt;&gt;&gt; MagicMock() != 3
True
&gt;&gt;&gt; mock = MagicMock()
&gt;&gt;&gt; mock.__eq__.return_value = True
&gt;&gt;&gt; mock == 3
True
</pre></div>
</div>
The return value of <code class="xref py py-meth docutils literal notranslate">MagicMock.__iter__()</code> can be any iterable object and isn’t
required to be an iterator:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = MagicMock()
&gt;&gt;&gt; mock.__iter__.return_value = [&#39;a&#39;, &#39;b&#39;, &#39;c&#39;]
&gt;&gt;&gt; list(mock)
[&#39;a&#39;, &#39;b&#39;, &#39;c&#39;]
&gt;&gt;&gt; list(mock)
[&#39;a&#39;, &#39;b&#39;, &#39;c&#39;]
</pre></div>
</div>
If the return value is an iterator, then iterating over it once will consume
it and subsequent iterations will result in an empty list:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock.__iter__.return_value = iter([&#39;a&#39;, &#39;b&#39;, &#39;c&#39;])
&gt;&gt;&gt; list(mock)
[&#39;a&#39;, &#39;b&#39;, &#39;c&#39;]
&gt;&gt;&gt; list(mock)
[]
</pre></div>
</div>
<code class="docutils literal notranslate">MagicMock</code> has all of the supported magic methods configured except for some
of the obscure and obsolete ones. You can still set these up if you want.
Magic methods that are supported but not setup by default in <code class="docutils literal notranslate">MagicMock</code> are:
<ul class="simple">
<li><code class="docutils literal notranslate">__subclasses__</code></li>
<li><code class="docutils literal notranslate">__dir__</code></li>
<li><code class="docutils literal notranslate">__format__</code></li>
<li><code class="docutils literal notranslate">__get__</code>, <code class="docutils literal notranslate">__set__</code> and <code class="docutils literal notranslate">__delete__</code></li>
<li><code class="docutils literal notranslate">__reversed__</code> and <code class="docutils literal notranslate">__missing__</code></li>
<li><code class="docutils literal notranslate">__reduce__</code>, <code class="docutils literal notranslate">__reduce_ex__</code>, <code class="docutils literal notranslate">__getinitargs__</code>, <code class="docutils literal notranslate">__getnewargs__</code>,
<code class="docutils literal notranslate">__getstate__</code> and <code class="docutils literal notranslate">__setstate__</code></li>
<li><code class="docutils literal notranslate">__getformat__</code> and <code class="docutils literal notranslate">__setformat__</code></li>
</ul>
<table class="docutils footnote" frame="void" id="id8" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id6">[2]</a></td><td>Magic methods should be looked up on the class rather than the
instance. Different versions of Python are inconsistent about applying this
rule. The supported protocol methods should work with all supported versions
of Python.</td></tr>
</tbody>
</table>
<table class="docutils footnote" frame="void" id="id9" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id7">[3]</a></td><td>The function is basically hooked up to the class, but each <code class="docutils literal notranslate">Mock</code>
instance is kept isolated from the others.</td></tr>
</tbody>
</table>
</div>
</div>
<div class="section" id="helpers">
<h2>26.5.5. Helpers<a class="headerlink" href="#helpers" title="Permalink to this headline">¶</a></h2>
<div class="section" id="sentinel">
<h3>26.5.5.1. sentinel<a class="headerlink" href="#sentinel" title="Permalink to this headline">¶</a></h3>
<dl class="data">
<dt id="unittest.mock.sentinel">
<code class="descclassname">unittest.mock.</code><code class="descname">sentinel</code><a class="headerlink" href="#unittest.mock.sentinel" title="Permalink to this definition">¶</a></dt>
<dd>The <code class="docutils literal notranslate">sentinel</code> object provides a convenient way of providing unique
objects for your tests.
Attributes are created on demand when you access them by name. Accessing
the same attribute will always return the same object. The objects
returned have a sensible repr so that test failure messages are readable.
<blockquote>
<div>The <code class="docutils literal notranslate">sentinel</code> attributes don’t preserve their identity when they are
<a class="reference internal" href="copy.html#module-copy" title="copy: Shallow and deep copy operations."><code class="xref py py-mod docutils literal notranslate">copied</code></a> or <a class="reference internal" href="pickle.html#module-pickle" title="pickle: Convert Python objects to streams of bytes and back."><code class="xref py py-mod docutils literal notranslate">pickled</code></a>.</div></blockquote>
</dd></dl>

Sometimes when testing you need to test that a specific object is passed as an
argument to another method, or returned. It can be common to create named
sentinel objects to test this. <a class="reference internal" href="#unittest.mock.sentinel" title="unittest.mock.sentinel"><code class="xref py py-data docutils literal notranslate">sentinel</code></a> provides a convenient way of
creating and testing the identity of objects like this.
In this example we monkey patch <code class="docutils literal notranslate">method</code> to return <code class="docutils literal notranslate">sentinel.some_object</code>:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; real = ProductionClass()
&gt;&gt;&gt; real.method = Mock(name=&quot;method&quot;)
&gt;&gt;&gt; real.method.return_value = sentinel.some_object
&gt;&gt;&gt; result = real.method()
&gt;&gt;&gt; assert result is sentinel.some_object
&gt;&gt;&gt; sentinel.some_object
sentinel.some_object
</pre></div>
</div>
</div>
<div class="section" id="default">
<h3>26.5.5.2. DEFAULT<a class="headerlink" href="#default" title="Permalink to this headline">¶</a></h3>
<dl class="data">
<dt id="unittest.mock.DEFAULT">
<code class="descclassname">unittest.mock.</code><code class="descname">DEFAULT</code><a class="headerlink" href="#unittest.mock.DEFAULT" title="Permalink to this definition">¶</a></dt>
<dd>The <a class="reference internal" href="#unittest.mock.DEFAULT" title="unittest.mock.DEFAULT"><code class="xref py py-data docutils literal notranslate">DEFAULT</code></a> object is a pre-created sentinel (actually
<code class="docutils literal notranslate">sentinel.DEFAULT</code>). It can be used by <a class="reference internal" href="#unittest.mock.Mock.side_effect" title="unittest.mock.Mock.side_effect"><code class="xref py py-attr docutils literal notranslate">side_effect</code></a>
functions to indicate that the normal return value should be used.
</dd></dl>

</div>
<div class="section" id="call">
<h3>26.5.5.3. call<a class="headerlink" href="#call" title="Permalink to this headline">¶</a></h3>
<dl class="function">
<dt id="unittest.mock.call">
<code class="descclassname">unittest.mock.</code><code class="descname">call</code>(*args, **kwargs)<a class="headerlink" href="#unittest.mock.call" title="Permalink to this definition">¶</a></dt>
<dd><a class="reference internal" href="#unittest.mock.call" title="unittest.mock.call"><code class="xref py py-func docutils literal notranslate">call()</code></a> is a helper object for making simpler assertions, for comparing with
<a class="reference internal" href="#unittest.mock.Mock.call_args" title="unittest.mock.Mock.call_args"><code class="xref py py-attr docutils literal notranslate">call_args</code></a>, <a class="reference internal" href="#unittest.mock.Mock.call_args_list" title="unittest.mock.Mock.call_args_list"><code class="xref py py-attr docutils literal notranslate">call_args_list</code></a>,
<a class="reference internal" href="#unittest.mock.Mock.mock_calls" title="unittest.mock.Mock.mock_calls"><code class="xref py py-attr docutils literal notranslate">mock_calls</code></a> and <a class="reference internal" href="#unittest.mock.Mock.method_calls" title="unittest.mock.Mock.method_calls"><code class="xref py py-attr docutils literal notranslate">method_calls</code></a>. <a class="reference internal" href="#unittest.mock.call" title="unittest.mock.call"><code class="xref py py-func docutils literal notranslate">call()</code></a> can also be
used with <a class="reference internal" href="#unittest.mock.Mock.assert_has_calls" title="unittest.mock.Mock.assert_has_calls"><code class="xref py py-meth docutils literal notranslate">assert_has_calls()</code></a>.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; m = MagicMock(return_value=None)
&gt;&gt;&gt; m(1, 2, a=&#39;foo&#39;, b=&#39;bar&#39;)
&gt;&gt;&gt; m()
&gt;&gt;&gt; m.call_args_list == [call(1, 2, a=&#39;foo&#39;, b=&#39;bar&#39;), call()]
True
</pre></div>
</div>
</dd></dl>

<dl class="method">
<dt id="unittest.mock.call.call_list">
<code class="descclassname">call.</code><code class="descname">call_list</code>()<a class="headerlink" href="#unittest.mock.call.call_list" title="Permalink to this definition">¶</a></dt>
<dd>For a call object that represents multiple calls, <a class="reference internal" href="#unittest.mock.call.call_list" title="unittest.mock.call.call_list"><code class="xref py py-meth docutils literal notranslate">call_list()</code></a>
returns a list of all the intermediate calls as well as the
final call.
</dd></dl>

<code class="docutils literal notranslate">call_list</code> is particularly useful for making assertions on “chained calls”. A
chained call is multiple calls on a single line of code. This results in
multiple entries in <a class="reference internal" href="#unittest.mock.Mock.mock_calls" title="unittest.mock.Mock.mock_calls"><code class="xref py py-attr docutils literal notranslate">mock_calls</code></a> on a mock. Manually constructing
the sequence of calls can be tedious.
<a class="reference internal" href="#unittest.mock.call.call_list" title="unittest.mock.call.call_list"><code class="xref py py-meth docutils literal notranslate">call_list()</code></a> can construct the sequence of calls from the same
chained call:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; m = MagicMock()
&gt;&gt;&gt; m(1).method(arg=&#39;foo&#39;).other(&#39;bar&#39;)(2.0)
&lt;MagicMock name=&#39;mock().method().other()()&#39; id=&#39;...&#39;&gt;
&gt;&gt;&gt; kall = call(1).method(arg=&#39;foo&#39;).other(&#39;bar&#39;)(2.0)
&gt;&gt;&gt; kall.call_list()
[call(1),
 call().method(arg=&#39;foo&#39;),
 call().method().other(&#39;bar&#39;),
 call().method().other()(2.0)]
&gt;&gt;&gt; m.mock_calls == kall.call_list()
True
</pre></div>
</div>
A <code class="docutils literal notranslate">call</code> object is either a tuple of (positional args, keyword args) or
(name, positional args, keyword args) depending on how it was constructed. When
you construct them yourself this isn’t particularly interesting, but the <code class="docutils literal notranslate">call</code>
objects that are in the <a class="reference internal" href="#unittest.mock.Mock.call_args" title="unittest.mock.Mock.call_args"><code class="xref py py-attr docutils literal notranslate">Mock.call_args</code></a>, <a class="reference internal" href="#unittest.mock.Mock.call_args_list" title="unittest.mock.Mock.call_args_list"><code class="xref py py-attr docutils literal notranslate">Mock.call_args_list</code></a> and
<a class="reference internal" href="#unittest.mock.Mock.mock_calls" title="unittest.mock.Mock.mock_calls"><code class="xref py py-attr docutils literal notranslate">Mock.mock_calls</code></a> attributes can be introspected to get at the individual
arguments they contain.
The <code class="docutils literal notranslate">call</code> objects in <a class="reference internal" href="#unittest.mock.Mock.call_args" title="unittest.mock.Mock.call_args"><code class="xref py py-attr docutils literal notranslate">Mock.call_args</code></a> and <a class="reference internal" href="#unittest.mock.Mock.call_args_list" title="unittest.mock.Mock.call_args_list"><code class="xref py py-attr docutils literal notranslate">Mock.call_args_list</code></a>
are two-tuples of (positional args, keyword args) whereas the <code class="docutils literal notranslate">call</code> objects
in <a class="reference internal" href="#unittest.mock.Mock.mock_calls" title="unittest.mock.Mock.mock_calls"><code class="xref py py-attr docutils literal notranslate">Mock.mock_calls</code></a>, along with ones you construct yourself, are
three-tuples of (name, positional args, keyword args).
You can use their “tupleness” to pull out the individual arguments for more
complex introspection and assertions. The positional arguments are a tuple
(an empty tuple if there are no positional arguments) and the keyword
arguments are a dictionary:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; m = MagicMock(return_value=None)
&gt;&gt;&gt; m(1, 2, 3, arg=&#39;one&#39;, arg2=&#39;two&#39;)
&gt;&gt;&gt; kall = m.call_args
&gt;&gt;&gt; args, kwargs = kall
&gt;&gt;&gt; args
(1, 2, 3)
&gt;&gt;&gt; kwargs
{&#39;arg2&#39;: &#39;two&#39;, &#39;arg&#39;: &#39;one&#39;}
&gt;&gt;&gt; args is kall[0]
True
&gt;&gt;&gt; kwargs is kall[1]
True
</pre></div>
</div>
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; m = MagicMock()
&gt;&gt;&gt; m.foo(4, 5, 6, arg=&#39;two&#39;, arg2=&#39;three&#39;)
&lt;MagicMock name=&#39;mock.foo()&#39; id=&#39;...&#39;&gt;
&gt;&gt;&gt; kall = m.mock_calls[0]
&gt;&gt;&gt; name, args, kwargs = kall
&gt;&gt;&gt; name
&#39;foo&#39;
&gt;&gt;&gt; args
(4, 5, 6)
&gt;&gt;&gt; kwargs
{&#39;arg2&#39;: &#39;three&#39;, &#39;arg&#39;: &#39;two&#39;}
&gt;&gt;&gt; name is m.mock_calls[0][0]
True
</pre></div>
</div>
</div>
<div class="section" id="create-autospec">
<h3>26.5.5.4. create_autospec<a class="headerlink" href="#create-autospec" title="Permalink to this headline">¶</a></h3>
<dl class="function">
<dt id="unittest.mock.create_autospec">
<code class="descclassname">unittest.mock.</code><code class="descname">create_autospec</code>(spec, spec_set=False, instance=False, **kwargs)<a class="headerlink" href="#unittest.mock.create_autospec" title="Permalink to this definition">¶</a></dt>
<dd>Create a mock object using another object as a spec. Attributes on the
mock will use the corresponding attribute on the spec object as their
spec.
Functions or methods being mocked will have their arguments checked to
ensure that they are called with the correct signature.
If spec_set is <code class="docutils literal notranslate">True</code> then attempting to set attributes that don’t exist
on the spec object will raise an <a class="reference internal" href="exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate">AttributeError</code></a>.
If a class is used as a spec then the return value of the mock (the
instance of the class) will have the same spec. You can use a class as the
spec for an instance object by passing <code class="docutils literal notranslate">instance=True</code>. The returned mock
will only be callable if instances of the mock are callable.
<a class="reference internal" href="#unittest.mock.create_autospec" title="unittest.mock.create_autospec"><code class="xref py py-func docutils literal notranslate">create_autospec()</code></a> also takes arbitrary keyword arguments that are passed to
the constructor of the created mock.
</dd></dl>

See <a class="reference internal" href="#auto-speccing">Autospeccing</a> for examples of how to use auto-speccing with
<a class="reference internal" href="#unittest.mock.create_autospec" title="unittest.mock.create_autospec"><code class="xref py py-func docutils literal notranslate">create_autospec()</code></a> and the autospec argument to <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a>.
</div>
<div class="section" id="any">
<h3>26.5.5.5. ANY<a class="headerlink" href="#any" title="Permalink to this headline">¶</a></h3>
<dl class="data">
<dt id="unittest.mock.ANY">
<code class="descclassname">unittest.mock.</code><code class="descname">ANY</code><a class="headerlink" href="#unittest.mock.ANY" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>

Sometimes you may need to make assertions about some of the arguments in a
call to mock, but either not care about some of the arguments or want to pull
them individually out of <a class="reference internal" href="#unittest.mock.Mock.call_args" title="unittest.mock.Mock.call_args"><code class="xref py py-attr docutils literal notranslate">call_args</code></a> and make more complex
assertions on them.
To ignore certain arguments you can pass in objects that compare equal to
everything. Calls to <a class="reference internal" href="#unittest.mock.Mock.assert_called_with" title="unittest.mock.Mock.assert_called_with"><code class="xref py py-meth docutils literal notranslate">assert_called_with()</code></a> and
<a class="reference internal" href="#unittest.mock.Mock.assert_called_once_with" title="unittest.mock.Mock.assert_called_once_with"><code class="xref py py-meth docutils literal notranslate">assert_called_once_with()</code></a> will then succeed no matter what was
passed in.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock(return_value=None)
&gt;&gt;&gt; mock(&#39;foo&#39;, bar=object())
&gt;&gt;&gt; mock.assert_called_once_with(&#39;foo&#39;, bar=ANY)
</pre></div>
</div>
<a class="reference internal" href="#unittest.mock.ANY" title="unittest.mock.ANY"><code class="xref py py-data docutils literal notranslate">ANY</code></a> can also be used in comparisons with call lists like
<a class="reference internal" href="#unittest.mock.Mock.mock_calls" title="unittest.mock.Mock.mock_calls"><code class="xref py py-attr docutils literal notranslate">mock_calls</code></a>:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; m = MagicMock(return_value=None)
&gt;&gt;&gt; m(1)
&gt;&gt;&gt; m(1, 2)
&gt;&gt;&gt; m(object())
&gt;&gt;&gt; m.mock_calls == [call(1), call(1, 2), ANY]
True
</pre></div>
</div>
</div>
<div class="section" id="filter-dir">
<h3>26.5.5.6. FILTER_DIR<a class="headerlink" href="#filter-dir" title="Permalink to this headline">¶</a></h3>
<dl class="data">
<dt id="unittest.mock.FILTER_DIR">
<code class="descclassname">unittest.mock.</code><code class="descname">FILTER_DIR</code><a class="headerlink" href="#unittest.mock.FILTER_DIR" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>

<a class="reference internal" href="#unittest.mock.FILTER_DIR" title="unittest.mock.FILTER_DIR"><code class="xref py py-data docutils literal notranslate">FILTER_DIR</code></a> is a module level variable that controls the way mock objects
respond to <a class="reference internal" href="functions.html#dir" title="dir"><code class="xref py py-func docutils literal notranslate">dir()</code></a> (only for Python 2.6 or more recent). The default is <code class="docutils literal notranslate">True</code>,
which uses the filtering described below, to only show useful members. If you
dislike this filtering, or need to switch it off for diagnostic purposes, then
set <code class="docutils literal notranslate">mock.FILTER_DIR = False</code>.
With filtering on, <code class="docutils literal notranslate">dir(some_mock)</code> shows only useful attributes and will
include any dynamically created attributes that wouldn’t normally be shown.
If the mock was created with a spec (or autospec of course) then all the
attributes from the original are shown, even if they haven’t been accessed
yet:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; dir(Mock())
[&#39;assert_any_call&#39;,
 &#39;assert_called_once_with&#39;,
 &#39;assert_called_with&#39;,
 &#39;assert_has_calls&#39;,
 &#39;attach_mock&#39;,
 ...
&gt;&gt;&gt; from urllib import request
&gt;&gt;&gt; dir(Mock(spec=request))
[&#39;AbstractBasicAuthHandler&#39;,
 &#39;AbstractDigestAuthHandler&#39;,
 &#39;AbstractHTTPHandler&#39;,
 &#39;BaseHandler&#39;,
 ...
</pre></div>
</div>
Many of the not-very-useful (private to <a class="reference internal" href="#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate">Mock</code></a> rather than the thing being
mocked) underscore and double underscore prefixed attributes have been
filtered from the result of calling <a class="reference internal" href="functions.html#dir" title="dir"><code class="xref py py-func docutils literal notranslate">dir()</code></a> on a <a class="reference internal" href="#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate">Mock</code></a>. If you dislike this
behaviour you can switch it off by setting the module level switch
<a class="reference internal" href="#unittest.mock.FILTER_DIR" title="unittest.mock.FILTER_DIR"><code class="xref py py-data docutils literal notranslate">FILTER_DIR</code></a>:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; from unittest import mock
&gt;&gt;&gt; mock.FILTER_DIR = False
&gt;&gt;&gt; dir(mock.Mock())
[&#39;_NonCallableMock__get_return_value&#39;,
 &#39;_NonCallableMock__get_side_effect&#39;,
 &#39;_NonCallableMock__return_value_doc&#39;,
 &#39;_NonCallableMock__set_return_value&#39;,
 &#39;_NonCallableMock__set_side_effect&#39;,
 &#39;__call__&#39;,
 &#39;__class__&#39;,
 ...
</pre></div>
</div>
Alternatively you can just use <code class="docutils literal notranslate">vars(my_mock)</code> (instance members) and
<code class="docutils literal notranslate">dir(type(my_mock))</code> (type members) to bypass the filtering irrespective of
<code class="xref py py-data docutils literal notranslate">mock.FILTER_DIR</code>.
</div>
<div class="section" id="mock-open">
<h3>26.5.5.7. mock_open<a class="headerlink" href="#mock-open" title="Permalink to this headline">¶</a></h3>
<dl class="function">
<dt id="unittest.mock.mock_open">
<code class="descclassname">unittest.mock.</code><code class="descname">mock_open</code>(mock=None, read_data=None)<a class="headerlink" href="#unittest.mock.mock_open" title="Permalink to this definition">¶</a></dt>
<dd>A helper function to create a mock to replace the use of <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate">open()</code></a>. It works
for <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate">open()</code></a> called directly or used as a context manager.
The mock argument is the mock object to configure. If <code class="docutils literal notranslate">None</code> (the
default) then a <a class="reference internal" href="#unittest.mock.MagicMock" title="unittest.mock.MagicMock"><code class="xref py py-class docutils literal notranslate">MagicMock</code></a> will be created for you, with the API limited
to methods or attributes available on standard file handles.
read_data is a string for the <code class="xref py py-meth docutils literal notranslate">read()</code>,
<a class="reference internal" href="io.html#io.IOBase.readline" title="io.IOBase.readline"><code class="xref py py-meth docutils literal notranslate">readline()</code></a>, and <a class="reference internal" href="io.html#io.IOBase.readlines" title="io.IOBase.readlines"><code class="xref py py-meth docutils literal notranslate">readlines()</code></a> methods
of the file handle to return. Calls to those methods will take data from
read_data until it is depleted. The mock of these methods is pretty
simplistic: every time the mock is called, the read_data is rewound to
the start. If you need more control over the data that you are feeding to
the tested code you will need to customize this mock for yourself. When that
is insufficient, one of the in-memory filesystem packages on <a class="reference external" href="https://pypi.org">PyPI</a> can offer a realistic filesystem for testing.
<div class="versionchanged">
Changed in version 3.4: Added <a class="reference internal" href="io.html#io.IOBase.readline" title="io.IOBase.readline"><code class="xref py py-meth docutils literal notranslate">readline()</code></a> and <a class="reference internal" href="io.html#io.IOBase.readlines" title="io.IOBase.readlines"><code class="xref py py-meth docutils literal notranslate">readlines()</code></a> support.
The mock of <code class="xref py py-meth docutils literal notranslate">read()</code> changed to consume read_data rather
than returning it on each call.
</div>
<div class="versionchanged">
Changed in version 3.5: read_data is now reset on each call to the mock.
</div>
</dd></dl>

Using <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate">open()</code></a> as a context manager is a great way to ensure your file handles
are closed properly and is becoming common:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>with open(&#39;/some/path&#39;, &#39;w&#39;) as f:
 f.write(&#39;something&#39;)
</pre></div>
</div>
The issue is that even if you mock out the call to <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-func docutils literal notranslate">open()</code></a> it is the
returned object that is used as a context manager (and has <a class="reference internal" href="../reference/datamodel.html#object.__enter__" title="object.__enter__"><code class="xref py py-meth docutils literal notranslate">__enter__()</code></a> and
<a class="reference internal" href="../reference/datamodel.html#object.__exit__" title="object.__exit__"><code class="xref py py-meth docutils literal notranslate">__exit__()</code></a> called).
Mocking context managers with a <a class="reference internal" href="#unittest.mock.MagicMock" title="unittest.mock.MagicMock"><code class="xref py py-class docutils literal notranslate">MagicMock</code></a> is common enough and fiddly
enough that a helper function is useful.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; m = mock_open()
&gt;&gt;&gt; with patch(&#39;__main__.open&#39;, m):
... with open(&#39;foo&#39;, &#39;w&#39;) as h:
... h.write(&#39;some stuff&#39;)
...
&gt;&gt;&gt; m.mock_calls
[call(&#39;foo&#39;, &#39;w&#39;),
 call().__enter__(),
 call().write(&#39;some stuff&#39;),
 call().__exit__(None, None, None)]
&gt;&gt;&gt; m.assert_called_once_with(&#39;foo&#39;, &#39;w&#39;)
&gt;&gt;&gt; handle = m()
&gt;&gt;&gt; handle.write.assert_called_once_with(&#39;some stuff&#39;)
</pre></div>
</div>
And for reading files:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; with patch(&#39;__main__.open&#39;, mock_open(read_data=&#39;bibble&#39;)) as m:
... with open(&#39;foo&#39;) as h:
... result = h.read()
...
&gt;&gt;&gt; m.assert_called_once_with(&#39;foo&#39;)
&gt;&gt;&gt; assert result == &#39;bibble&#39;
</pre></div>
</div>
</div>
<div class="section" id="autospeccing">
<h3>26.5.5.8. Autospeccing<a class="headerlink" href="#autospeccing" title="Permalink to this headline">¶</a></h3>
Autospeccing is based on the existing <code class="xref py py-attr docutils literal notranslate">spec</code> feature of mock. It limits the
api of mocks to the api of an original object (the spec), but it is recursive
(implemented lazily) so that attributes of mocks only have the same api as
the attributes of the spec. In addition mocked functions / methods have the
same call signature as the original so they raise a <a class="reference internal" href="exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate">TypeError</code></a> if they are
called incorrectly.
Before I explain how auto-speccing works, here’s why it is needed.
<a class="reference internal" href="#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate">Mock</code></a> is a very powerful and flexible object, but it suffers from two flaws
when used to mock out objects from a system under test. One of these flaws is
specific to the <a class="reference internal" href="#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate">Mock</code></a> api and the other is a more general problem with using
mock objects.
First the problem specific to <a class="reference internal" href="#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate">Mock</code></a>. <a class="reference internal" href="#unittest.mock.Mock" title="unittest.mock.Mock"><code class="xref py py-class docutils literal notranslate">Mock</code></a> has two assert methods that are
extremely handy: <a class="reference internal" href="#unittest.mock.Mock.assert_called_with" title="unittest.mock.Mock.assert_called_with"><code class="xref py py-meth docutils literal notranslate">assert_called_with()</code></a> and
<a class="reference internal" href="#unittest.mock.Mock.assert_called_once_with" title="unittest.mock.Mock.assert_called_once_with"><code class="xref py py-meth docutils literal notranslate">assert_called_once_with()</code></a>.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock(name=&#39;Thing&#39;, return_value=None)
&gt;&gt;&gt; mock(1, 2, 3)
&gt;&gt;&gt; mock.assert_called_once_with(1, 2, 3)
&gt;&gt;&gt; mock(1, 2, 3)
&gt;&gt;&gt; mock.assert_called_once_with(1, 2, 3)
Traceback (most recent call last):
 ...
AssertionError: Expected &#39;mock&#39; to be called once. Called 2 times.
</pre></div>
</div>
Because mocks auto-create attributes on demand, and allow you to call them
with arbitrary arguments, if you misspell one of these assert methods then
your assertion is gone:
<div class="highlight-pycon notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock = Mock(name=&#39;Thing&#39;, return_value=None)
&gt;&gt;&gt; mock(1, 2, 3)
&gt;&gt;&gt; mock.assret_called_once_with(4, 5, 6)
</pre></div>
</div>
Your tests can pass silently and incorrectly because of the typo.
The second issue is more general to mocking. If you refactor some of your
code, rename members and so on, any tests for code that is still using the
old api but uses mocks instead of the real objects will still pass. This
means your tests can all pass even though your code is broken.
Note that this is another reason why you need integration tests as well as
unit tests. Testing everything in isolation is all fine and dandy, but if you
don’t test how your units are “wired together” there is still lots of room
for bugs that tests might have caught.
<code class="xref py py-mod docutils literal notranslate">mock</code> already provides a feature to help with this, called speccing. If you
use a class or instance as the <code class="xref py py-attr docutils literal notranslate">spec</code> for a mock then you can only access
attributes on the mock that exist on the real class:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; from urllib import request
&gt;&gt;&gt; mock = Mock(spec=request.Request)
&gt;&gt;&gt; mock.assret_called_with
Traceback (most recent call last):
 ...
AttributeError: Mock object has no attribute &#39;assret_called_with&#39;
</pre></div>
</div>
The spec only applies to the mock itself, so we still have the same issue
with any methods on the mock:
<div class="highlight-pycon notranslate"><div class="highlight"><pre>&gt;&gt;&gt; mock.has_data()
&lt;mock.Mock object at 0x...&gt;
&gt;&gt;&gt; mock.has_data.assret_called_with()
</pre></div>
</div>
Auto-speccing solves this problem. You can either pass <code class="docutils literal notranslate">autospec=True</code> to
<a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> / <a class="reference internal" href="#unittest.mock.patch.object" title="unittest.mock.patch.object"><code class="xref py py-func docutils literal notranslate">patch.object()</code></a> or use the <a class="reference internal" href="#unittest.mock.create_autospec" title="unittest.mock.create_autospec"><code class="xref py py-func docutils literal notranslate">create_autospec()</code></a> function to create a
mock with a spec. If you use the <code class="docutils literal notranslate">autospec=True</code> argument to <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> then the
object that is being replaced will be used as the spec object. Because the
speccing is done “lazily” (the spec is created as attributes on the mock are
accessed) you can use it with very complex or deeply nested objects (like
modules that import modules that import modules) without a big performance
hit.
Here’s an example of it in use:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; from urllib import request
&gt;&gt;&gt; patcher = patch(&#39;__main__.request&#39;, autospec=True)
&gt;&gt;&gt; mock_request = patcher.start()
&gt;&gt;&gt; request is mock_request
True
&gt;&gt;&gt; mock_request.Request
&lt;MagicMock name=&#39;request.Request&#39; spec=&#39;Request&#39; id=&#39;...&#39;&gt;
</pre></div>
</div>
You can see that <code class="xref py py-class docutils literal notranslate">request.Request</code> has a spec. <code class="xref py py-class docutils literal notranslate">request.Request</code> takes two
arguments in the constructor (one of which is self). Here’s what happens if
we try to call it incorrectly:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; req = request.Request()
Traceback (most recent call last):
 ...
TypeError: &lt;lambda&gt;() takes at least 2 arguments (1 given)
</pre></div>
</div>
The spec also applies to instantiated classes (i.e. the return value of
specced mocks):
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; req = request.Request(&#39;foo&#39;)
&gt;&gt;&gt; req
&lt;NonCallableMagicMock name=&#39;request.Request()&#39; spec=&#39;Request&#39; id=&#39;...&#39;&gt;
</pre></div>
</div>
<code class="xref py py-class docutils literal notranslate">Request</code> objects are not callable, so the return value of instantiating our
mocked out <code class="xref py py-class docutils literal notranslate">request.Request</code> is a non-callable mock. With the spec in place
any typos in our asserts will raise the correct error:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; req.add_header(&#39;spam&#39;, &#39;eggs&#39;)
&lt;MagicMock name=&#39;request.Request().add_header()&#39; id=&#39;...&#39;&gt;
&gt;&gt;&gt; req.add_header.assret_called_with
Traceback (most recent call last):
 ...
AttributeError: Mock object has no attribute &#39;assret_called_with&#39;
&gt;&gt;&gt; req.add_header.assert_called_with(&#39;spam&#39;, &#39;eggs&#39;)
</pre></div>
</div>
In many cases you will just be able to add <code class="docutils literal notranslate">autospec=True</code> to your existing
<a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> calls and then be protected against bugs due to typos and api
changes.
As well as using autospec through <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> there is a
<a class="reference internal" href="#unittest.mock.create_autospec" title="unittest.mock.create_autospec"><code class="xref py py-func docutils literal notranslate">create_autospec()</code></a> for creating autospecced mocks directly:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; from urllib import request
&gt;&gt;&gt; mock_request = create_autospec(request)
&gt;&gt;&gt; mock_request.Request(&#39;foo&#39;, &#39;bar&#39;)
&lt;NonCallableMagicMock name=&#39;mock.Request()&#39; spec=&#39;Request&#39; id=&#39;...&#39;&gt;
</pre></div>
</div>
This isn’t without caveats and limitations however, which is why it is not
the default behaviour. In order to know what attributes are available on the
spec object, autospec has to introspect (access attributes) the spec. As you
traverse attributes on the mock a corresponding traversal of the original
object is happening under the hood. If any of your specced objects have
properties or descriptors that can trigger code execution then you may not be
able to use autospec. On the other hand it is much better to design your
objects so that introspection is safe <a class="footnote-reference" href="#id11" id="id10">[4]</a>.
A more serious problem is that it is common for instance attributes to be
created in the <a class="reference internal" href="../reference/datamodel.html#object.__init__" title="object.__init__"><code class="xref py py-meth docutils literal notranslate">__init__()</code></a> method and not to exist on the class at all.
autospec can’t know about any dynamically created attributes and restricts
the api to visible attributes.
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class Something:
... def __init__(self):
... self.a = 33
...
&gt;&gt;&gt; with patch(&#39;__main__.Something&#39;, autospec=True):
... thing = Something()
... thing.a
...
Traceback (most recent call last):
 ...
AttributeError: Mock object has no attribute &#39;a&#39;
</pre></div>
</div>
There are a few different ways of resolving this problem. The easiest, but
not necessarily the least annoying, way is to simply set the required
attributes on the mock after creation. Just because autospec doesn’t allow
you to fetch attributes that don’t exist on the spec it doesn’t prevent you
setting them:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; with patch(&#39;__main__.Something&#39;, autospec=True):
... thing = Something()
... thing.a = 33
...
</pre></div>
</div>
There is a more aggressive version of both spec and autospec that does
prevent you setting non-existent attributes. This is useful if you want to
ensure your code only sets valid attributes too, but obviously it prevents
this particular scenario:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; with patch(&#39;__main__.Something&#39;, autospec=True, spec_set=True):
... thing = Something()
... thing.a = 33
...
Traceback (most recent call last):
 ...
AttributeError: Mock object has no attribute &#39;a&#39;
</pre></div>
</div>
Probably the best way of solving the problem is to add class attributes as
default values for instance members initialised in <a class="reference internal" href="../reference/datamodel.html#object.__init__" title="object.__init__"><code class="xref py py-meth docutils literal notranslate">__init__()</code></a>. Note that if
you are only setting default attributes in <a class="reference internal" href="../reference/datamodel.html#object.__init__" title="object.__init__"><code class="xref py py-meth docutils literal notranslate">__init__()</code></a> then providing them via
class attributes (shared between instances of course) is faster too. e.g.
<div class="highlight-python notranslate"><div class="highlight"><pre>class Something:
 a = 33
</pre></div>
</div>
This brings up another issue. It is relatively common to provide a default
value of <code class="docutils literal notranslate">None</code> for members that will later be an object of a different type.
<code class="docutils literal notranslate">None</code> would be useless as a spec because it wouldn’t let you access any
attributes or methods on it. As <code class="docutils literal notranslate">None</code> is never going to be useful as a
spec, and probably indicates a member that will normally of some other type,
autospec doesn’t use a spec for members that are set to <code class="docutils literal notranslate">None</code>. These will
just be ordinary mocks (well - MagicMocks):
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class Something:
... member = None
...
&gt;&gt;&gt; mock = create_autospec(Something)
&gt;&gt;&gt; mock.member.foo.bar.baz()
&lt;MagicMock name=&#39;mock.member.foo.bar.baz()&#39; id=&#39;...&#39;&gt;
</pre></div>
</div>
If modifying your production classes to add defaults isn’t to your liking
then there are more options. One of these is simply to use an instance as the
spec rather than the class. The other is to create a subclass of the
production class and add the defaults to the subclass without affecting the
production class. Both of these require you to use an alternative object as
the spec. Thankfully <a class="reference internal" href="#unittest.mock.patch" title="unittest.mock.patch"><code class="xref py py-func docutils literal notranslate">patch()</code></a> supports this - you can simply pass the
alternative object as the autospec argument:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class Something:
... def __init__(self):
... self.a = 33
...
&gt;&gt;&gt; class SomethingForTest(Something):
... a = 33
...
&gt;&gt;&gt; p = patch(&#39;__main__.Something&#39;, autospec=SomethingForTest)
&gt;&gt;&gt; mock = p.start()
&gt;&gt;&gt; mock.a
&lt;NonCallableMagicMock name=&#39;Something.a&#39; spec=&#39;int&#39; id=&#39;...&#39;&gt;
</pre></div>
</div>
<table class="docutils footnote" frame="void" id="id11" rules="none">
<colgroup><col class="label" /><col /></colgroup>
<tbody valign="top">
<tr><td class="label"><a class="fn-backref" href="#id10">[4]</a></td><td>This only applies to classes or already instantiated objects. Calling
a mocked class to create a mock instance does not create a real instance.
It is only attribute lookups - along with calls to <a class="reference internal" href="functions.html#dir" title="dir"><code class="xref py py-func docutils literal notranslate">dir()</code></a> - that are done.</td></tr>
</tbody>
</table>
</div>
</div>
</div>

</div>
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 <div class="sphinxsidebar" role="navigation" aria-label="main navigation">
 <div class="sphinxsidebarwrapper">
 <h3><a href="../contents.html">Table Of Contents</a></h3>
 <ul>
<li><a class="reference internal" href="#">26.5. <code class="docutils literal notranslate">unittest.mock</code> — mock object library</a><ul>
<li><a class="reference internal" href="#quick-guide">26.5.1. Quick Guide</a></li>
<li><a class="reference internal" href="#the-mock-class">26.5.2. The Mock Class</a><ul>
<li><a class="reference internal" href="#calling">26.5.2.1. Calling</a></li>
<li><a class="reference internal" href="#deleting-attributes">26.5.2.2. Deleting Attributes</a></li>
<li><a class="reference internal" href="#mock-names-and-the-name-attribute">26.5.2.3. Mock names and the name attribute</a></li>
<li><a class="reference internal" href="#attaching-mocks-as-attributes">26.5.2.4. Attaching Mocks as Attributes</a></li>
</ul>
</li>
<li><a class="reference internal" href="#the-patchers">26.5.3. The patchers</a><ul>
<li><a class="reference internal" href="#patch">26.5.3.1. patch</a></li>
<li><a class="reference internal" href="#patch-object">26.5.3.2. patch.object</a></li>
<li><a class="reference internal" href="#patch-dict">26.5.3.3. patch.dict</a></li>
<li><a class="reference internal" href="#patch-multiple">26.5.3.4. patch.multiple</a></li>
<li><a class="reference internal" href="#patch-methods-start-and-stop">26.5.3.5. patch methods: start and stop</a></li>
<li><a class="reference internal" href="#patch-builtins">26.5.3.6. patch builtins</a></li>
<li><a class="reference internal" href="#test-prefix">26.5.3.7. TEST_PREFIX</a></li>
<li><a class="reference internal" href="#nesting-patch-decorators">26.5.3.8. Nesting Patch Decorators</a></li>
<li><a class="reference internal" href="#where-to-patch">26.5.3.9. Where to patch</a></li>
<li><a class="reference internal" href="#patching-descriptors-and-proxy-objects">26.5.3.10. Patching Descriptors and Proxy Objects</a></li>
</ul>
</li>
<li><a class="reference internal" href="#magicmock-and-magic-method-support">26.5.4. MagicMock and magic method support</a><ul>
<li><a class="reference internal" href="#mocking-magic-methods">26.5.4.1. Mocking Magic Methods</a></li>
<li><a class="reference internal" href="#magic-mock">26.5.4.2. Magic Mock</a></li>
</ul>
</li>
<li><a class="reference internal" href="#helpers">26.5.5. Helpers</a><ul>
<li><a class="reference internal" href="#sentinel">26.5.5.1. sentinel</a></li>
<li><a class="reference internal" href="#default">26.5.5.2. DEFAULT</a></li>
<li><a class="reference internal" href="#call">26.5.5.3. call</a></li>
<li><a class="reference internal" href="#create-autospec">26.5.5.4. create_autospec</a></li>
<li><a class="reference internal" href="#any">26.5.5.5. ANY</a></li>
<li><a class="reference internal" href="#filter-dir">26.5.5.6. FILTER_DIR</a></li>
<li><a class="reference internal" href="#mock-open">26.5.5.7. mock_open</a></li>
<li><a class="reference internal" href="#autospeccing">26.5.5.8. Autospeccing</a></li>
</ul>
</li>
</ul>
</li>
</ul>

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