===========
pytest-mock
===========
This plugin provides a ``mocker`` fixture which is a thin-wrapper around the patching API
provided by the `mock package <http://pypi.python.org/pypi/mock>`_:
.. code-block:: python
import os
class UnixFS:
@staticmethod
def rm(filename):
os.remove(filename)
def test_unix_fs(mocker):
mocker.patch('os.remove')
UnixFS.rm('file')
os.remove.assert_called_once_with('file')
Besides undoing the mocking automatically after the end of the test, it also provides other
nice utilities such as ``spy`` and ``stub``, and uses pytest introspection when
comparing calls.
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`Professionally supported pytest-mock is now available <https://tidelift.com/subscription/pkg/pypi-pytest_mock?utm_source=pypi-pytest-mock&utm_medium=referral&utm_campaign=readme>`_
Usage
=====
The ``mocker`` fixture has the same API as
`mock.patch <https://docs.python.org/3/library/unittest.mock.html#patch>`_,
supporting the same arguments:
.. code-block:: python
def test_foo(mocker):
# all valid calls
mocker.patch('os.remove')
mocker.patch.object(os, 'listdir', autospec=True)
mocked_isfile = mocker.patch('os.path.isfile')
The supported methods are:
* `mocker.patch <https://docs.python.org/3/library/unittest.mock.html#patch>`_
* `mocker.patch.object <https://docs.python.org/3/library/unittest.mock.html#patch-object>`_
* `mocker.patch.multiple <https://docs.python.org/3/library/unittest.mock.html#patch-multiple>`_
* `mocker.patch.dict <https://docs.python.org/3/library/unittest.mock.html#patch-dict>`_
* `mocker.stopall <https://docs.python.org/3/library/unittest.mock.html#unittest.mock.patch.stopall>`_
* ``mocker.resetall()``: calls `reset_mock() <https://docs.python.org/3/library/unittest.mock.html#unittest.mock.Mock.reset_mock>`_ in all mocked objects up to this point.
Also, as a convenience, these names from the ``mock`` module are accessible directly from ``mocker``:
* `Mock <https://docs.python.org/3/library/unittest.mock.html#unittest.mock.Mock>`_
* `MagicMock <https://docs.python.org/3/library/unittest.mock.html#unittest.mock.MagicMock>`_
* `PropertyMock <https://docs.python.org/3/library/unittest.mock.html#unittest.mock.PropertyMock>`_
* `ANY <https://docs.python.org/3/library/unittest.mock.html#any>`_
* `DEFAULT <https://docs.python.org/3/library/unittest.mock.html#default>`_ *(Version 1.4)*
* `call <https://docs.python.org/3/library/unittest.mock.html#call>`_ *(Version 1.1)*
* `sentinel <https://docs.python.org/3/library/unittest.mock.html#sentinel>`_ *(Version 1.2)*
* `mock_open <https://docs.python.org/3/library/unittest.mock.html#mock-open>`_
* `seal <https://docs.python.org/3/library/unittest.mock.html#unittest.mock.seal>`_ *(Version 3.4)*
It is also possible to use mocking functionality from fixtures of other scopes using
the appropriate mock fixture:
* ``class_mocker``
* ``module_mocker``
* ``package_mocker``
* ``session_mocker``
Type Annotations
----------------
*New in version 3.3.0.*
``pytest-mock`` is fully type annotated, letting users use static type checkers to
test their code.
The ``mocker`` fixture returns ``pytest_mock.MockerFixture`` which can be used
to annotate test functions:
.. code-block:: python
from pytest_mock import MockerFixture
def test_foo(mocker: MockerFixture) -> None:
...
The type annotations have been checked with ``mypy``, which is the only
type checker supported at the moment; other type-checkers might work
but are not currently tested.
Spy
---
The ``mocker.spy`` object acts exactly like the original method in all cases, except the spy
also tracks function/method calls, return values and exceptions raised.
.. code-block:: python
def test_spy_method(mocker):
class Foo(object):
def bar(self, v):
return v * 2
foo = Foo()
spy = mocker.spy(foo, 'bar')
assert foo.bar(21) == 42
spy.assert_called_once_with(21)
assert spy.spy_return == 42
def test_spy_function(mocker):
# mymodule declares `myfunction` which just returns 42
import mymodule
spy = mocker.spy(mymodule, "myfunction")
assert mymodule.myfunction() == 42
assert spy.call_count == 1
assert spy.spy_return == 42
The object returned by ``mocker.spy`` is a ``MagicMock`` object, so all standard checking functions
are available (like ``assert_called_once_with`` or ``call_count`` in the examples above).
In addition, spy objects contain two extra attributes:
* ``spy_return``: contains the returned value of the spied function.
* ``spy_exception``: contain the last exception value raised by the spied function/method when
it was last called, or ``None`` if no exception was raised.
Besides functions and normal methods, ``mocker.spy`` also works for class and static methods.
As of version 3.0.0, ``mocker.spy`` also works with ``async def`` functions.
.. note::
In versions earlier than ``2.0``, the attributes were called ``return_value`` and
``side_effect`` respectively, but due to incompatibilities with ``unittest.mock``
they had to be renamed (see `#175`_ for details).
.. _#175: https://github.com/pytest-dev/pytest-mock/issues/175
Stub
----
The stub is a mock object that accepts any arguments and is useful to test callbacks.
It may receive an optional name that is shown in its ``repr``, useful for debugging.
.. code-block:: python
def test_stub(mocker):
def foo(on_something):
on_something('foo', 'bar')
stub = mocker.stub(name='on_something_stub')
foo(stub)
stub.assert_called_once_with('foo', 'bar')
Improved reporting of mock call assertion errors
------------------------------------------------
This plugin monkeypatches the mock library to improve pytest output for failures
of mock call assertions like ``Mock.assert_called_with()`` by hiding internal traceback
entries from the ``mock`` module.
It also adds introspection information on differing call arguments when
calling the helper methods. This features catches `AssertionError` raised in
the method, and uses pytest's own `advanced assertions`_ to return a better
diff::
mocker = <pytest_mock.MockerFixture object at 0x0381E2D0>
def test(mocker):
m = mocker.Mock()
m('fo')
> m.assert_called_once_with('', bar=4)
E AssertionError: Expected call: mock('', bar=4)
E Actual call: mock('fo')
E
E pytest introspection follows:
E
E Args:
E assert ('fo',) == ('',)
E At index 0 diff: 'fo' != ''
E Use -v to get the full diff
E Kwargs:
E assert {} == {'bar': 4}
E Right contains more items:
E {'bar': 4}
E Use -v to get the full diff
test_foo.py:6: AssertionError
========================== 1 failed in 0.03 seconds ===========================
This is useful when asserting mock calls with many/nested arguments and trying
to quickly see the difference.
This feature is probably safe, but if you encounter any problems it can be disabled in
your ``pytest.ini`` file:
.. code-block:: ini
[pytest]
mock_traceback_monkeypatch = false
Note that this feature is automatically disabled with the ``--tb=native`` option. The underlying
mechanism used to suppress traceback entries from ``mock`` module does not work with that option
anyway plus it generates confusing messages on Python 3.5 due to exception chaining
.. _advanced assertions: http://docs.pytest.org/en/stable/assert.html
Use standalone "mock" package
-----------------------------
*New in version 1.4.0.*
Python 3 users might want to use a newest version of the ``mock`` package as published on PyPI
than the one that comes with the Python distribution.
.. code-block:: ini
[pytest]
mock_use_standalone_module = true
This will force the plugin to import ``mock`` instead of the ``unittest.mock`` module bundled with
Python 3.4+. Note that this option is only used in Python 3+, as Python 2 users only have the option
to use the ``mock`` package from PyPI anyway.
Note about usage as context manager
-----------------------------------
Although mocker's API is intentionally the same as ``mock.patch``'s, its use
as context manager and function decorator is **not** supported through the
fixture:
.. code-block:: python
def test_context_manager(mocker):
a = A()
with mocker.patch.object(a, 'doIt', return_value=True, autospec=True): # DO NOT DO THIS
assert a.doIt() == True
The purpose of this plugin is to make the use of context managers and
function decorators for mocking unnecessary, so it will emit a warning when used as such.
If you really intend to mock a context manager, ``mocker.patch.context_manager`` exists
which won't issue the above warning.
Install
=======
Install using `pip <http://pip-installer.org/>`_:
.. code-block:: console
$ pip install pytest-mock
Changelog
=========
Please consult the `changelog page`_.
.. _changelog page: https://github.com/pytest-dev/pytest-mock/blob/master/CHANGELOG.rst
Why bother with a plugin?
=========================
There are a number of different ``patch`` usages in the standard ``mock`` API,
but IMHO they don't scale very well when you have more than one or two
patches to apply.
It may lead to an excessive nesting of ``with`` statements, breaking the flow
of the test:
.. code-block:: python
import mock
def test_unix_fs():
with mock.patch('os.remove'):
UnixFS.rm('file')
os.remove.assert_called_once_with('file')
with mock.patch('os.listdir'):
assert UnixFS.ls('dir') == expected
# ...
with mock.patch('shutil.copy'):
UnixFS.cp('src', 'dst')
# ...
One can use ``patch`` as a decorator to improve the flow of the test:
.. code-block:: python
@mock.patch('os.remove')
@mock.patch('os.listdir')
@mock.patch('shutil.copy')
def test_unix_fs(mocked_copy, mocked_listdir, mocked_remove):
UnixFS.rm('file')
os.remove.assert_called_once_with('file')
assert UnixFS.ls('dir') == expected
# ...
UnixFS.cp('src', 'dst')
# ...
But this poses a few disadvantages:
- test functions must receive the mock objects as parameter, even if you don't plan to
access them directly; also, order depends on the order of the decorated ``patch``
functions;
- receiving the mocks as parameters doesn't mix nicely with pytest's approach of
naming fixtures as parameters, or ``pytest.mark.parametrize``;
- you can't easily undo the mocking during the test execution;
An alternative is to use ``contextlib.ExitStack`` to stack the context managers in a single level of indentation
to improve the flow of the test:
.. code-block:: python
import contextlib
import mock
def test_unix_fs():
with contextlib.ExitStack() as stack:
stack.enter_context(mock.patch('os.remove'))
UnixFS.rm('file')
os.remove.assert_called_once_with('file')
stack.enter_context(mock.patch('os.listdir'))
assert UnixFS.ls('dir') == expected
# ...
stack.enter_context(mock.patch('shutil.copy'))
UnixFS.cp('src', 'dst')
# ...
But this is arguably a little more complex than using ``pytest-mock``.
Contributing
============
Contributions are welcome! After cloning the repository, create a virtual env
and install ``pytest-mock`` in editable mode with ``dev`` extras:
.. code-block:: console
$ pip install --editable .[dev]
$ pre-commit install
Tests are run with ``tox``, you can run the baseline environments before submitting a PR:
.. code-block:: console
$ tox -e py38,linting
Style checks and formatting are done automatically during commit courtesy of
`pre-commit <https://pre-commit.com>`_.
License
=======
Distributed under the terms of the `MIT`_ license.
Security contact information
============================
To report a security vulnerability, please use the `Tidelift security contact <https://tidelift.com/security>`__. Tidelift will coordinate the fix and disclosure.
.. _MIT: https://github.com/pytest-dev/pytest-mock/blob/master/LICENSE
