| mock 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. |
| |
| mock is now part of the Python standard library, available as `unittest.mock |
| <http://docs.python.org/py3k/library/unittest.mock.html#module-unittest.mock>`_ |
| in Python 3.3 onwards. |
| |
| mock provides a core `MagicMock` 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. |
| |
| mock is tested on Python versions 2.5-2.7 and Python 3. mock is also tested |
| with the latest versions of Jython and pypy. |
| |
| The mock module also provides utility functions / objects to assist with |
| testing, particularly monkey patching. |
| |
| * `PDF documentation for 1.0.1 |
| <http://www.voidspace.org.uk/downloads/mock-1.0.1.pdf>`_ |
| * `mock on google code (repository and issue tracker) |
| <http://code.google.com/p/mock/>`_ |
| * `mock documentation |
| <http://www.voidspace.org.uk/python/mock/>`_ |
| * `mock on PyPI <http://pypi.python.org/pypi/mock/>`_ |
| * `Mailing list (testing-in-python@lists.idyll.org) |
| <http://lists.idyll.org/listinfo/testing-in-python>`_ |
| |
| Mock is very easy to use and is designed for use with |
| `unittest <http://pypi.python.org/pypi/unittest2>`_. Mock is based on |
| the 'action -> assertion' pattern instead of 'record -> replay' used by many |
| mocking frameworks. See the `mock documentation`_ for full details. |
| |
| Mock 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:: |
| |
| >>> from mock import Mock |
| >>> real = ProductionClass() |
| >>> real.method = Mock(return_value=3) |
| >>> real.method(3, 4, 5, key='value') |
| 3 |
| >>> real.method.assert_called_with(3, 4, 5, key='value') |
| |
| `side_effect` allows you to perform side effects, return different values or |
| raise an exception when a mock is called:: |
| |
| >>> mock = Mock(side_effect=KeyError('foo')) |
| >>> mock() |
| Traceback (most recent call last): |
| ... |
| KeyError: 'foo' |
| >>> values = {'a': 1, 'b': 2, 'c': 3} |
| >>> def side_effect(arg): |
| ... return values[arg] |
| ... |
| >>> mock.side_effect = side_effect |
| >>> mock('a'), mock('b'), mock('c') |
| (3, 2, 1) |
| >>> mock.side_effect = [5, 4, 3, 2, 1] |
| >>> mock(), mock(), mock() |
| (5, 4, 3) |
| |
| 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 `AttributeError`. |
| |
| The `patch` 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:: |
| |
| >>> from mock import patch |
| >>> @patch('test_module.ClassName1') |
| ... @patch('test_module.ClassName2') |
| ... def test(MockClass2, MockClass1): |
| ... test_module.ClassName1() |
| ... test_module.ClassName2() |
| |
| ... assert MockClass1.called |
| ... assert MockClass2.called |
| ... |
| >>> test() |
| |
| .. 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 `test_module.ClassName2` is passed in first. |
| |
| With `patch` it matters that you patch objects in the namespace where they |
| are looked up. This is normally straightforward, but for a quick guide |
| read `where to patch |
| <http://www.voidspace.org.uk/python/mock/patch.html#where-to-patch>`_. |
| |
| As well as a decorator `patch` can be used as a context manager in a with |
| statement:: |
| |
| >>> with patch.object(ProductionClass, 'method') as mock_method: |
| ... mock_method.return_value = None |
| ... real = ProductionClass() |
| ... real.method(1, 2, 3) |
| ... |
| >>> mock_method.assert_called_once_with(1, 2, 3) |
| |
| There is also `patch.dict` for setting values in a dictionary just during the |
| scope of a test and restoring the dictionary to its original state when the |
| test ends:: |
| |
| >>> foo = {'key': 'value'} |
| >>> original = foo.copy() |
| >>> with patch.dict(foo, {'newkey': 'newvalue'}, clear=True): |
| ... assert foo == {'newkey': 'newvalue'} |
| ... |
| >>> assert foo == original |
| |
| Mock supports the mocking of Python magic methods. The easiest way of |
| using magic methods is with the `MagicMock` class. It allows you to do |
| things like:: |
| |
| >>> from mock import MagicMock |
| >>> mock = MagicMock() |
| >>> mock.__str__.return_value = 'foobarbaz' |
| >>> str(mock) |
| 'foobarbaz' |
| >>> mock.__str__.assert_called_once_with() |
| |
| Mock allows you to assign functions (or other Mock instances) to magic methods |
| and they will be called appropriately. The MagicMock 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:: |
| |
| >>> from mock import Mock |
| >>> mock = Mock() |
| >>> mock.__str__ = Mock(return_value = 'wheeeeee') |
| >>> str(mock) |
| 'wheeeeee' |
| |
| For ensuring that the mock objects your tests use have the same api as the |
| objects they are replacing, you can use "auto-speccing". Auto-speccing can |
| be done through the `autospec` argument to patch, or the `create_autospec` |
| 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:: |
| |
| >>> from mock import create_autospec |
| >>> def function(a, b, c): |
| ... pass |
| ... |
| >>> mock_function = create_autospec(function, return_value='fishy') |
| >>> mock_function(1, 2, 3) |
| 'fishy' |
| >>> mock_function.assert_called_once_with(1, 2, 3) |
| >>> mock_function('wrong arguments') |
| Traceback (most recent call last): |
| ... |
| TypeError: <lambda>() takes exactly 3 arguments (1 given) |
| |
| `create_autospec` can also be used on classes, where it copies the signature of |
| the `__init__` method, and on callable objects where it copies the signature of |
| the `__call__` method. |
| |
| The distribution contains tests and documentation. The tests require |
| `unittest2 <http://pypi.python.org/pypi/unittest2>`_ to run on Python 2.5, 2.6 |
| or 3.1. For Python 2.7 and 3.2 they can be run with |
| `python -m unittest discover`. |
| |
| Docs from the in-development version of `mock` can be found at |
| `mock.readthedocs.org <http://mock.readthedocs.org>`_. |