diff options
author | Michael Foord <michael@voidspace.org.uk> | 2012-03-28 13:36:02 (GMT) |
---|---|---|
committer | Michael Foord <michael@voidspace.org.uk> | 2012-03-28 13:36:02 (GMT) |
commit | a9e6fb201dc1746b1394a804095fe58e35829a6f (patch) | |
tree | 4fc3912a2b41b9ac72e571e8cd69cc560dfaad4f /Doc/library | |
parent | ad95c2d25c5fe5c4c88b73de2c60722ba56572e9 (diff) | |
download | cpython-a9e6fb201dc1746b1394a804095fe58e35829a6f.zip cpython-a9e6fb201dc1746b1394a804095fe58e35829a6f.tar.gz cpython-a9e6fb201dc1746b1394a804095fe58e35829a6f.tar.bz2 |
Unsplit unittest.mock documentation
Diffstat (limited to 'Doc/library')
-rw-r--r-- | Doc/library/development.rst | 4 | ||||
-rw-r--r-- | Doc/library/unittest.mock-examples.rst | 425 | ||||
-rw-r--r-- | Doc/library/unittest.mock-getting-started.rst | 419 | ||||
-rw-r--r-- | Doc/library/unittest.mock-helpers.rst | 537 | ||||
-rw-r--r-- | Doc/library/unittest.mock-magicmethods.rst | 226 | ||||
-rw-r--r-- | Doc/library/unittest.mock-patch.rst | 538 | ||||
-rw-r--r-- | Doc/library/unittest.mock.rst | 1285 |
7 files changed, 1701 insertions, 1733 deletions
diff --git a/Doc/library/development.rst b/Doc/library/development.rst index 79c5dd9..06e7048 100644 --- a/Doc/library/development.rst +++ b/Doc/library/development.rst @@ -20,10 +20,6 @@ The list of modules described in this chapter is: doctest.rst unittest.rst unittest.mock.rst - unittest.mock-patch.rst - unittest.mock-magicmethods.rst - unittest.mock-helpers.rst - unittest.mock-getting-started.rst unittest.mock-examples.rst 2to3.rst test.rst diff --git a/Doc/library/unittest.mock-examples.rst b/Doc/library/unittest.mock-examples.rst index 4b6616c..a561fdc 100644 --- a/Doc/library/unittest.mock-examples.rst +++ b/Doc/library/unittest.mock-examples.rst @@ -1,18 +1,427 @@ -.. _further-examples: - -:mod:`unittest.mock` --- further examples -========================================= +:mod:`unittest.mock` --- getting started +======================================== -.. module:: unittest.mock - :synopsis: Mock object library. .. moduleauthor:: Michael Foord <michael@python.org> .. currentmodule:: unittest.mock .. versionadded:: 3.3 -Here are some more examples for some slightly more advanced scenarios than in -the :ref:`getting started <getting-started>` guide. +.. _getting-started: + +Using Mock +---------- + +Mock Patching Methods +~~~~~~~~~~~~~~~~~~~~~ + +Common uses for :class:`Mock` objects include: + +* Patching methods +* Recording method calls on objects + +You might want to replace a method on an object to check that +it is called with the correct arguments by another part of the system: + + >>> real = SomeClass() + >>> real.method = MagicMock(name='method') + >>> real.method(3, 4, 5, key='value') + <MagicMock name='method()' id='...'> + +Once our mock has been used (`real.method` in this example) it has methods +and attributes that allow you to make assertions about how it has been used. + +.. note:: + + In most of these examples the :class:`Mock` and :class:`MagicMock` classes + are interchangeable. As the `MagicMock` is the more capable class it makes + a sensible one to use by default. + +Once the mock has been called its :attr:`~Mock.called` attribute is set to +`True`. More importantly we can use the :meth:`~Mock.assert_called_with` or +:meth`~Mock.assert_called_once_with` method to check that it was called with +the correct arguments. + +This example tests that calling `ProductionClass().method` results in a call to +the `something` method: + + >>> class ProductionClass(object): + ... def method(self): + ... self.something(1, 2, 3) + ... def something(self, a, b, c): + ... pass + ... + >>> real = ProductionClass() + >>> real.something = MagicMock() + >>> real.method() + >>> real.something.assert_called_once_with(1, 2, 3) + + + +Mock for Method Calls on an Object +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +In the last example we patched a method directly on an object to check that it +was called correctly. Another common use case is to pass an object into a +method (or some part of the system under test) and then check that it is used +in the correct way. + +The simple `ProductionClass` below has a `closer` method. If it is called with +an object then it calls `close` on it. + + >>> class ProductionClass(object): + ... def closer(self, something): + ... something.close() + ... + +So to test it we need to pass in an object with a `close` method and check +that it was called correctly. + + >>> real = ProductionClass() + >>> mock = Mock() + >>> real.closer(mock) + >>> mock.close.assert_called_with() + +We don't have to do any work to provide the 'close' method on our mock. +Accessing close creates it. So, if 'close' hasn't already been called then +accessing it in the test will create it, but :meth:`~Mock.assert_called_with` +will raise a failure exception. + + +Mocking Classes +~~~~~~~~~~~~~~~ + +A common use case is to mock out classes instantiated by your code under test. +When you patch a class, then that class is replaced with a mock. Instances +are created by *calling the class*. This means you access the "mock instance" +by looking at the return value of the mocked class. + +In the example below we have a function `some_function` that instantiates `Foo` +and calls a method on it. The call to `patch` replaces the class `Foo` with a +mock. The `Foo` instance is the result of calling the mock, so it is configured +by modify the mock :attr:`~Mock.return_value`. + + >>> def some_function(): + ... instance = module.Foo() + ... return instance.method() + ... + >>> with patch('module.Foo') as mock: + ... instance = mock.return_value + ... instance.method.return_value = 'the result' + ... result = some_function() + ... assert result == 'the result' + + +Naming your mocks +~~~~~~~~~~~~~~~~~ + +It can be useful to give your mocks a name. The name is shown in the repr of +the mock and can be helpful when the mock appears in test failure messages. The +name is also propagated to attributes or methods of the mock: + + >>> mock = MagicMock(name='foo') + >>> mock + <MagicMock name='foo' id='...'> + >>> mock.method + <MagicMock name='foo.method' id='...'> + + +Tracking all Calls +~~~~~~~~~~~~~~~~~~ + +Often you want to track more than a single call to a method. The +:attr:`~Mock.mock_calls` attribute records all calls +to child attributes of the mock - and also to their children. + + >>> mock = MagicMock() + >>> mock.method() + <MagicMock name='mock.method()' id='...'> + >>> mock.attribute.method(10, x=53) + <MagicMock name='mock.attribute.method()' id='...'> + >>> mock.mock_calls + [call.method(), call.attribute.method(10, x=53)] + +If you make an assertion about `mock_calls` and any unexpected methods +have been called, then the assertion will fail. This is useful because as well +as asserting that the calls you expected have been made, you are also checking +that they were made in the right order and with no additional calls: + +You use the :data:`call` object to construct lists for comparing with +`mock_calls`: + + >>> expected = [call.method(), call.attribute.method(10, x=53)] + >>> mock.mock_calls == expected + True + + +Setting Return Values and Attributes +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Setting the return values on a mock object is trivially easy: + + >>> mock = Mock() + >>> mock.return_value = 3 + >>> mock() + 3 + +Of course you can do the same for methods on the mock: + + >>> mock = Mock() + >>> mock.method.return_value = 3 + >>> mock.method() + 3 + +The return value can also be set in the constructor: + + >>> mock = Mock(return_value=3) + >>> mock() + 3 + +If you need an attribute setting on your mock, just do it: + + >>> mock = Mock() + >>> mock.x = 3 + >>> mock.x + 3 + +Sometimes you want to mock up a more complex situation, like for example +`mock.connection.cursor().execute("SELECT 1")`. If we wanted this call to +return a list, then we have to configure the result of the nested call. + +We can use :data:`call` to construct the set of calls in a "chained call" like +this for easy assertion afterwards: + + >>> mock = Mock() + >>> cursor = mock.connection.cursor.return_value + >>> cursor.execute.return_value = ['foo'] + >>> mock.connection.cursor().execute("SELECT 1") + ['foo'] + >>> expected = call.connection.cursor().execute("SELECT 1").call_list() + >>> mock.mock_calls + [call.connection.cursor(), call.connection.cursor().execute('SELECT 1')] + >>> mock.mock_calls == expected + True + +It is the call to `.call_list()` that turns our call object into a list of +calls representing the chained calls. + + +Raising exceptions with mocks +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +A useful attribute is :attr:`~Mock.side_effect`. If you set this to an +exception class or instance then the exception will be raised when the mock +is called. + + >>> mock = Mock(side_effect=Exception('Boom!')) + >>> mock() + Traceback (most recent call last): + ... + Exception: Boom! + + +Side effect functions and iterables +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +`side_effect` can also be set to a function or an iterable. The use case for +`side_effect` as an iterable is where your mock is going to be called several +times, and you want each call to return a different value. When you set +`side_effect` to an iterable every call to the mock returns the next value +from the iterable: + + >>> mock = MagicMock(side_effect=[4, 5, 6]) + >>> mock() + 4 + >>> mock() + 5 + >>> mock() + 6 + + +For more advanced use cases, like dynamically varying the return values +depending on what the mock is called with, `side_effect` can be a function. +The function will be called with the same arguments as the mock. Whatever the +function returns is what the call returns: + + >>> vals = {(1, 2): 1, (2, 3): 2} + >>> def side_effect(*args): + ... return vals[args] + ... + >>> mock = MagicMock(side_effect=side_effect) + >>> mock(1, 2) + 1 + >>> mock(2, 3) + 2 + + +Creating a Mock from an Existing Object +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +One problem with over use of mocking is that it couples your tests to the +implementation of your mocks rather than your real code. Suppose you have a +class that implements `some_method`. In a test for another class, you +provide a mock of this object that *also* provides `some_method`. If later +you refactor the first class, so that it no longer has `some_method` - then +your tests will continue to pass even though your code is now broken! + +`Mock` allows you to provide an object as a specification for the mock, +using the `spec` keyword argument. Accessing methods / attributes on the +mock that don't exist on your specification object will immediately raise an +attribute error. If you change the implementation of your specification, then +tests that use that class will start failing immediately without you having to +instantiate the class in those tests. + + >>> mock = Mock(spec=SomeClass) + >>> mock.old_method() + Traceback (most recent call last): + ... + AttributeError: object has no attribute 'old_method' + +If you want a stronger form of specification that prevents the setting +of arbitrary attributes as well as the getting of them then you can use +`spec_set` instead of `spec`. + + + +Patch Decorators +---------------- + +.. note:: + + 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 :ref:`where to patch <where-to-patch>`. + + +A common need in tests is to patch a class attribute or a module attribute, +for example patching a builtin or patching a class in a module to test that it +is instantiated. Modules and classes are effectively global, so patching on +them has to be undone after the test or the patch will persist into other +tests and cause hard to diagnose problems. + +mock provides three convenient decorators for this: `patch`, `patch.object` and +`patch.dict`. `patch` takes a single string, of the form +`package.module.Class.attribute` to specify the attribute you are patching. It +also optionally takes a value that you want the attribute (or class or +whatever) to be replaced with. 'patch.object' takes an object and the name of +the attribute you would like patched, plus optionally the value to patch it +with. + +`patch.object`: + + >>> original = SomeClass.attribute + >>> @patch.object(SomeClass, 'attribute', sentinel.attribute) + ... def test(): + ... assert SomeClass.attribute == sentinel.attribute + ... + >>> test() + >>> assert SomeClass.attribute == original + + >>> @patch('package.module.attribute', sentinel.attribute) + ... def test(): + ... from package.module import attribute + ... assert attribute is sentinel.attribute + ... + >>> test() + +If you are patching a module (including `__builtin__`) then use `patch` +instead of `patch.object`: + + >>> mock = MagicMock(return_value = sentinel.file_handle) + >>> with patch('__builtin__.open', mock): + ... handle = open('filename', 'r') + ... + >>> mock.assert_called_with('filename', 'r') + >>> assert handle == sentinel.file_handle, "incorrect file handle returned" + +The module name can be 'dotted', in the form `package.module` if needed: + + >>> @patch('package.module.ClassName.attribute', sentinel.attribute) + ... def test(): + ... from package.module import ClassName + ... assert ClassName.attribute == sentinel.attribute + ... + >>> test() + +A nice pattern is to actually decorate test methods themselves: + + >>> class MyTest(unittest2.TestCase): + ... @patch.object(SomeClass, 'attribute', sentinel.attribute) + ... def test_something(self): + ... self.assertEqual(SomeClass.attribute, sentinel.attribute) + ... + >>> original = SomeClass.attribute + >>> MyTest('test_something').test_something() + >>> assert SomeClass.attribute == original + +If you want to patch with a Mock, you can use `patch` with only one argument +(or `patch.object` with two arguments). The mock will be created for you and +passed into the test function / method: + + >>> class MyTest(unittest2.TestCase): + ... @patch.object(SomeClass, 'static_method') + ... def test_something(self, mock_method): + ... SomeClass.static_method() + ... mock_method.assert_called_with() + ... + >>> MyTest('test_something').test_something() + +You can stack up multiple patch decorators using this pattern: + + >>> class MyTest(unittest2.TestCase): + ... @patch('package.module.ClassName1') + ... @patch('package.module.ClassName2') + ... def test_something(self, MockClass2, MockClass1): + ... self.assertTrue(package.module.ClassName1 is MockClass1) + ... self.assertTrue(package.module.ClassName2 is MockClass2) + ... + >>> MyTest('test_something').test_something() + +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. + +There is also :func:`patch.dict` for setting values in a dictionary just +during a scope 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 + +`patch`, `patch.object` and `patch.dict` can all be used as context managers. + +Where you use `patch` to create a mock for you, you can get a reference to the +mock using the "as" form of the with statement: + + >>> class ProductionClass(object): + ... def method(self): + ... pass + ... + >>> with patch.object(ProductionClass, 'method') as mock_method: + ... mock_method.return_value = None + ... real = ProductionClass() + ... real.method(1, 2, 3) + ... + >>> mock_method.assert_called_with(1, 2, 3) + + +As an alternative `patch`, `patch.object` and `patch.dict` can be used as +class decorators. When used in this way it is the same as applying the +decorator indvidually to every method whose name starts with "test". + + +.. _further-examples: + +Further Examples +================ + + +Here are some more examples for some slightly more advanced scenarios. Mocking chained calls diff --git a/Doc/library/unittest.mock-getting-started.rst b/Doc/library/unittest.mock-getting-started.rst deleted file mode 100644 index 850a894..0000000 --- a/Doc/library/unittest.mock-getting-started.rst +++ /dev/null @@ -1,419 +0,0 @@ -:mod:`unittest.mock` --- getting started -======================================== - -.. module:: unittest.mock - :synopsis: Mock object library. -.. moduleauthor:: Michael Foord <michael@python.org> -.. currentmodule:: unittest.mock - -.. versionadded:: 3.3 - - -.. _getting-started: - -Using Mock ----------- - -Mock Patching Methods -~~~~~~~~~~~~~~~~~~~~~ - -Common uses for :class:`Mock` objects include: - -* Patching methods -* Recording method calls on objects - -You might want to replace a method on an object to check that -it is called with the correct arguments by another part of the system: - - >>> real = SomeClass() - >>> real.method = MagicMock(name='method') - >>> real.method(3, 4, 5, key='value') - <MagicMock name='method()' id='...'> - -Once our mock has been used (`real.method` in this example) it has methods -and attributes that allow you to make assertions about how it has been used. - -.. note:: - - In most of these examples the :class:`Mock` and :class:`MagicMock` classes - are interchangeable. As the `MagicMock` is the more capable class it makes - a sensible one to use by default. - -Once the mock has been called its :attr:`~Mock.called` attribute is set to -`True`. More importantly we can use the :meth:`~Mock.assert_called_with` or -:meth`~Mock.assert_called_once_with` method to check that it was called with -the correct arguments. - -This example tests that calling `ProductionClass().method` results in a call to -the `something` method: - - >>> class ProductionClass(object): - ... def method(self): - ... self.something(1, 2, 3) - ... def something(self, a, b, c): - ... pass - ... - >>> real = ProductionClass() - >>> real.something = MagicMock() - >>> real.method() - >>> real.something.assert_called_once_with(1, 2, 3) - - - -Mock for Method Calls on an Object -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - -In the last example we patched a method directly on an object to check that it -was called correctly. Another common use case is to pass an object into a -method (or some part of the system under test) and then check that it is used -in the correct way. - -The simple `ProductionClass` below has a `closer` method. If it is called with -an object then it calls `close` on it. - - >>> class ProductionClass(object): - ... def closer(self, something): - ... something.close() - ... - -So to test it we need to pass in an object with a `close` method and check -that it was called correctly. - - >>> real = ProductionClass() - >>> mock = Mock() - >>> real.closer(mock) - >>> mock.close.assert_called_with() - -We don't have to do any work to provide the 'close' method on our mock. -Accessing close creates it. So, if 'close' hasn't already been called then -accessing it in the test will create it, but :meth:`~Mock.assert_called_with` -will raise a failure exception. - - -Mocking Classes -~~~~~~~~~~~~~~~ - -A common use case is to mock out classes instantiated by your code under test. -When you patch a class, then that class is replaced with a mock. Instances -are created by *calling the class*. This means you access the "mock instance" -by looking at the return value of the mocked class. - -In the example below we have a function `some_function` that instantiates `Foo` -and calls a method on it. The call to `patch` replaces the class `Foo` with a -mock. The `Foo` instance is the result of calling the mock, so it is configured -by modify the mock :attr:`~Mock.return_value`. - - >>> def some_function(): - ... instance = module.Foo() - ... return instance.method() - ... - >>> with patch('module.Foo') as mock: - ... instance = mock.return_value - ... instance.method.return_value = 'the result' - ... result = some_function() - ... assert result == 'the result' - - -Naming your mocks -~~~~~~~~~~~~~~~~~ - -It can be useful to give your mocks a name. The name is shown in the repr of -the mock and can be helpful when the mock appears in test failure messages. The -name is also propagated to attributes or methods of the mock: - - >>> mock = MagicMock(name='foo') - >>> mock - <MagicMock name='foo' id='...'> - >>> mock.method - <MagicMock name='foo.method' id='...'> - - -Tracking all Calls -~~~~~~~~~~~~~~~~~~ - -Often you want to track more than a single call to a method. The -:attr:`~Mock.mock_calls` attribute records all calls -to child attributes of the mock - and also to their children. - - >>> mock = MagicMock() - >>> mock.method() - <MagicMock name='mock.method()' id='...'> - >>> mock.attribute.method(10, x=53) - <MagicMock name='mock.attribute.method()' id='...'> - >>> mock.mock_calls - [call.method(), call.attribute.method(10, x=53)] - -If you make an assertion about `mock_calls` and any unexpected methods -have been called, then the assertion will fail. This is useful because as well -as asserting that the calls you expected have been made, you are also checking -that they were made in the right order and with no additional calls: - -You use the :data:`call` object to construct lists for comparing with -`mock_calls`: - - >>> expected = [call.method(), call.attribute.method(10, x=53)] - >>> mock.mock_calls == expected - True - - -Setting Return Values and Attributes -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - -Setting the return values on a mock object is trivially easy: - - >>> mock = Mock() - >>> mock.return_value = 3 - >>> mock() - 3 - -Of course you can do the same for methods on the mock: - - >>> mock = Mock() - >>> mock.method.return_value = 3 - >>> mock.method() - 3 - -The return value can also be set in the constructor: - - >>> mock = Mock(return_value=3) - >>> mock() - 3 - -If you need an attribute setting on your mock, just do it: - - >>> mock = Mock() - >>> mock.x = 3 - >>> mock.x - 3 - -Sometimes you want to mock up a more complex situation, like for example -`mock.connection.cursor().execute("SELECT 1")`. If we wanted this call to -return a list, then we have to configure the result of the nested call. - -We can use :data:`call` to construct the set of calls in a "chained call" like -this for easy assertion afterwards: - - >>> mock = Mock() - >>> cursor = mock.connection.cursor.return_value - >>> cursor.execute.return_value = ['foo'] - >>> mock.connection.cursor().execute("SELECT 1") - ['foo'] - >>> expected = call.connection.cursor().execute("SELECT 1").call_list() - >>> mock.mock_calls - [call.connection.cursor(), call.connection.cursor().execute('SELECT 1')] - >>> mock.mock_calls == expected - True - -It is the call to `.call_list()` that turns our call object into a list of -calls representing the chained calls. - - -Raising exceptions with mocks -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - -A useful attribute is :attr:`~Mock.side_effect`. If you set this to an -exception class or instance then the exception will be raised when the mock -is called. - - >>> mock = Mock(side_effect=Exception('Boom!')) - >>> mock() - Traceback (most recent call last): - ... - Exception: Boom! - - -Side effect functions and iterables -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - -`side_effect` can also be set to a function or an iterable. The use case for -`side_effect` as an iterable is where your mock is going to be called several -times, and you want each call to return a different value. When you set -`side_effect` to an iterable every call to the mock returns the next value -from the iterable: - - >>> mock = MagicMock(side_effect=[4, 5, 6]) - >>> mock() - 4 - >>> mock() - 5 - >>> mock() - 6 - - -For more advanced use cases, like dynamically varying the return values -depending on what the mock is called with, `side_effect` can be a function. -The function will be called with the same arguments as the mock. Whatever the -function returns is what the call returns: - - >>> vals = {(1, 2): 1, (2, 3): 2} - >>> def side_effect(*args): - ... return vals[args] - ... - >>> mock = MagicMock(side_effect=side_effect) - >>> mock(1, 2) - 1 - >>> mock(2, 3) - 2 - - -Creating a Mock from an Existing Object -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - -One problem with over use of mocking is that it couples your tests to the -implementation of your mocks rather than your real code. Suppose you have a -class that implements `some_method`. In a test for another class, you -provide a mock of this object that *also* provides `some_method`. If later -you refactor the first class, so that it no longer has `some_method` - then -your tests will continue to pass even though your code is now broken! - -`Mock` allows you to provide an object as a specification for the mock, -using the `spec` keyword argument. Accessing methods / attributes on the -mock that don't exist on your specification object will immediately raise an -attribute error. If you change the implementation of your specification, then -tests that use that class will start failing immediately without you having to -instantiate the class in those tests. - - >>> mock = Mock(spec=SomeClass) - >>> mock.old_method() - Traceback (most recent call last): - ... - AttributeError: object has no attribute 'old_method' - -If you want a stronger form of specification that prevents the setting -of arbitrary attributes as well as the getting of them then you can use -`spec_set` instead of `spec`. - - - -Patch Decorators ----------------- - -.. note:: - - 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 :ref:`where to patch <where-to-patch>`. - - -A common need in tests is to patch a class attribute or a module attribute, -for example patching a builtin or patching a class in a module to test that it -is instantiated. Modules and classes are effectively global, so patching on -them has to be undone after the test or the patch will persist into other -tests and cause hard to diagnose problems. - -mock provides three convenient decorators for this: `patch`, `patch.object` and -`patch.dict`. `patch` takes a single string, of the form -`package.module.Class.attribute` to specify the attribute you are patching. It -also optionally takes a value that you want the attribute (or class or -whatever) to be replaced with. 'patch.object' takes an object and the name of -the attribute you would like patched, plus optionally the value to patch it -with. - -`patch.object`: - - >>> original = SomeClass.attribute - >>> @patch.object(SomeClass, 'attribute', sentinel.attribute) - ... def test(): - ... assert SomeClass.attribute == sentinel.attribute - ... - >>> test() - >>> assert SomeClass.attribute == original - - >>> @patch('package.module.attribute', sentinel.attribute) - ... def test(): - ... from package.module import attribute - ... assert attribute is sentinel.attribute - ... - >>> test() - -If you are patching a module (including `__builtin__`) then use `patch` -instead of `patch.object`: - - >>> mock = MagicMock(return_value = sentinel.file_handle) - >>> with patch('__builtin__.open', mock): - ... handle = open('filename', 'r') - ... - >>> mock.assert_called_with('filename', 'r') - >>> assert handle == sentinel.file_handle, "incorrect file handle returned" - -The module name can be 'dotted', in the form `package.module` if needed: - - >>> @patch('package.module.ClassName.attribute', sentinel.attribute) - ... def test(): - ... from package.module import ClassName - ... assert ClassName.attribute == sentinel.attribute - ... - >>> test() - -A nice pattern is to actually decorate test methods themselves: - - >>> class MyTest(unittest2.TestCase): - ... @patch.object(SomeClass, 'attribute', sentinel.attribute) - ... def test_something(self): - ... self.assertEqual(SomeClass.attribute, sentinel.attribute) - ... - >>> original = SomeClass.attribute - >>> MyTest('test_something').test_something() - >>> assert SomeClass.attribute == original - -If you want to patch with a Mock, you can use `patch` with only one argument -(or `patch.object` with two arguments). The mock will be created for you and -passed into the test function / method: - - >>> class MyTest(unittest2.TestCase): - ... @patch.object(SomeClass, 'static_method') - ... def test_something(self, mock_method): - ... SomeClass.static_method() - ... mock_method.assert_called_with() - ... - >>> MyTest('test_something').test_something() - -You can stack up multiple patch decorators using this pattern: - - >>> class MyTest(unittest2.TestCase): - ... @patch('package.module.ClassName1') - ... @patch('package.module.ClassName2') - ... def test_something(self, MockClass2, MockClass1): - ... self.assertTrue(package.module.ClassName1 is MockClass1) - ... self.assertTrue(package.module.ClassName2 is MockClass2) - ... - >>> MyTest('test_something').test_something() - -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. - -There is also :func:`patch.dict` for setting values in a dictionary just -during a scope 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 - -`patch`, `patch.object` and `patch.dict` can all be used as context managers. - -Where you use `patch` to create a mock for you, you can get a reference to the -mock using the "as" form of the with statement: - - >>> class ProductionClass(object): - ... def method(self): - ... pass - ... - >>> with patch.object(ProductionClass, 'method') as mock_method: - ... mock_method.return_value = None - ... real = ProductionClass() - ... real.method(1, 2, 3) - ... - >>> mock_method.assert_called_with(1, 2, 3) - - -As an alternative `patch`, `patch.object` and `patch.dict` can be used as -class decorators. When used in this way it is the same as applying the -decorator indvidually to every method whose name starts with "test". - -For some more advanced examples, see the :ref:`further-examples` page. diff --git a/Doc/library/unittest.mock-helpers.rst b/Doc/library/unittest.mock-helpers.rst deleted file mode 100644 index 6c68a48..0000000 --- a/Doc/library/unittest.mock-helpers.rst +++ /dev/null @@ -1,537 +0,0 @@ -:mod:`unittest.mock` --- helpers -================================ - -.. module:: unittest.mock - :synopsis: Mock object library. -.. moduleauthor:: Michael Foord <michael@python.org> -.. currentmodule:: unittest.mock - -.. versionadded:: 3.3 - - -sentinel --------- - -.. data:: sentinel - - The ``sentinel`` 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. - -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. `sentinel` provides a convenient way of -creating and testing the identity of objects like this. - -In this example we monkey patch `method` to return `sentinel.some_object`: - - >>> real = ProductionClass() - >>> real.method = Mock(name="method") - >>> real.method.return_value = sentinel.some_object - >>> result = real.method() - >>> assert result is sentinel.some_object - >>> sentinel.some_object - sentinel.some_object - - -DEFAULT -------- - - -.. data:: DEFAULT - - The `DEFAULT` object is a pre-created sentinel (actually - `sentinel.DEFAULT`). It can be used by :attr:`~Mock.side_effect` - functions to indicate that the normal return value should be used. - - - -call ----- - -.. function:: call(*args, **kwargs) - - `call` is a helper object for making simpler assertions, for comparing - with :attr:`~Mock.call_args`, :attr:`~Mock.call_args_list`, - :attr:`~Mock.mock_calls` and:attr: `~Mock.method_calls`. `call` can also be - used with :meth:`~Mock.assert_has_calls`. - - >>> m = MagicMock(return_value=None) - >>> m(1, 2, a='foo', b='bar') - >>> m() - >>> m.call_args_list == [call(1, 2, a='foo', b='bar'), call()] - True - -.. method:: call.call_list() - - For a call object that represents multiple calls, `call_list` - returns a list of all the intermediate calls as well as the - final call. - -`call_list` 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 :attr:`~Mock.mock_calls` on a mock. Manually constructing -the sequence of calls can be tedious. - -:meth:`~call.call_list` can construct the sequence of calls from the same -chained call: - - >>> m = MagicMock() - >>> m(1).method(arg='foo').other('bar')(2.0) - <MagicMock name='mock().method().other()()' id='...'> - >>> kall = call(1).method(arg='foo').other('bar')(2.0) - >>> kall.call_list() - [call(1), - call().method(arg='foo'), - call().method().other('bar'), - call().method().other()(2.0)] - >>> m.mock_calls == kall.call_list() - True - -.. _calls-as-tuples: - -A `call` 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 `call` -objects that are in the :attr:`Mock.call_args`, :attr:`Mock.call_args_list` and -:attr:`Mock.mock_calls` attributes can be introspected to get at the individual -arguments they contain. - -The `call` objects in :attr:`Mock.call_args` and :attr:`Mock.call_args_list` -are two-tuples of (positional args, keyword args) whereas the `call` objects -in :attr:`Mock.mock_calls`, 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: - - >>> m = MagicMock(return_value=None) - >>> m(1, 2, 3, arg='one', arg2='two') - >>> kall = m.call_args - >>> args, kwargs = kall - >>> args - (1, 2, 3) - >>> kwargs - {'arg2': 'two', 'arg': 'one'} - >>> args is kall[0] - True - >>> kwargs is kall[1] - True - - >>> m = MagicMock() - >>> m.foo(4, 5, 6, arg='two', arg2='three') - <MagicMock name='mock.foo()' id='...'> - >>> kall = m.mock_calls[0] - >>> name, args, kwargs = kall - >>> name - 'foo' - >>> args - (4, 5, 6) - >>> kwargs - {'arg2': 'three', 'arg': 'two'} - >>> name is m.mock_calls[0][0] - True - - -create_autospec ---------------- - -.. function:: create_autospec(spec, spec_set=False, instance=False, **kwargs) - - 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 `True` then attempting to set attributes that don't exist - on the spec object will raise an `AttributeError`. - - 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 `instance=True`. The returned mock - will only be callable if instances of the mock are callable. - - `create_autospec` also takes arbitrary keyword arguments that are passed to - the constructor of the created mock. - -See :ref:`auto-speccing` for examples of how to use auto-speccing with -`create_autospec` and the `autospec` argument to :func:`patch`. - - -ANY ---- - -.. data:: ANY - -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 :attr:`~Mock.call_args` and make more complex -assertions on them. - -To ignore certain arguments you can pass in objects that compare equal to -*everything*. Calls to :meth:`~Mock.assert_called_with` and -:meth:`~Mock.assert_called_once_with` will then succeed no matter what was -passed in. - - >>> mock = Mock(return_value=None) - >>> mock('foo', bar=object()) - >>> mock.assert_called_once_with('foo', bar=ANY) - -`ANY` can also be used in comparisons with call lists like -:attr:`~Mock.mock_calls`: - - >>> m = MagicMock(return_value=None) - >>> m(1) - >>> m(1, 2) - >>> m(object()) - >>> m.mock_calls == [call(1), call(1, 2), ANY] - True - - - -FILTER_DIR ----------- - -.. data:: FILTER_DIR - -`FILTER_DIR` is a module level variable that controls the way mock objects -respond to `dir` (only for Python 2.6 or more recent). The default is `True`, -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 `mock.FILTER_DIR = False`. - -With filtering on, `dir(some_mock)` 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: - - >>> dir(Mock()) - ['assert_any_call', - 'assert_called_once_with', - 'assert_called_with', - 'assert_has_calls', - 'attach_mock', - ... - >>> from urllib import request - >>> dir(Mock(spec=request)) - ['AbstractBasicAuthHandler', - 'AbstractDigestAuthHandler', - 'AbstractHTTPHandler', - 'BaseHandler', - ... - -Many of the not-very-useful (private to `Mock` rather than the thing being -mocked) underscore and double underscore prefixed attributes have been -filtered from the result of calling `dir` on a `Mock`. If you dislike this -behaviour you can switch it off by setting the module level switch -`FILTER_DIR`: - - >>> from unittest import mock - >>> mock.FILTER_DIR = False - >>> dir(mock.Mock()) - ['_NonCallableMock__get_return_value', - '_NonCallableMock__get_side_effect', - '_NonCallableMock__return_value_doc', - '_NonCallableMock__set_return_value', - '_NonCallableMock__set_side_effect', - '__call__', - '__class__', - ... - -Alternatively you can just use `vars(my_mock)` (instance members) and -`dir(type(my_mock))` (type members) to bypass the filtering irrespective of -`mock.FILTER_DIR`. - - -mock_open ---------- - -.. function:: mock_open(mock=None, read_data=None) - - A helper function to create a mock to replace the use of `open`. It works - for `open` called directly or used as a context manager. - - The `mock` argument is the mock object to configure. If `None` (the - default) then a `MagicMock` 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 `read` method of the file handle to return. - This is an empty string by default. - -Using `open` as a context manager is a great way to ensure your file handles -are closed properly and is becoming common:: - - with open('/some/path', 'w') as f: - f.write('something') - -The issue is that even if you mock out the call to `open` it is the -*returned object* that is used as a context manager (and has `__enter__` and -`__exit__` called). - -Mocking context managers with a :class:`MagicMock` is common enough and fiddly -enough that a helper function is useful. - - >>> m = mock_open() - >>> with patch('__main__.open', m, create=True): - ... with open('foo', 'w') as h: - ... h.write('some stuff') - ... - >>> m.mock_calls - [call('foo', 'w'), - call().__enter__(), - call().write('some stuff'), - call().__exit__(None, None, None)] - >>> m.assert_called_once_with('foo', 'w') - >>> handle = m() - >>> handle.write.assert_called_once_with('some stuff') - -And for reading files: - - >>> with patch('__main__.open', mock_open(read_data='bibble'), create=True) as m: - ... with open('foo') as h: - ... result = h.read() - ... - >>> m.assert_called_once_with('foo') - >>> assert result == 'bibble' - - -.. _auto-speccing: - -Autospeccing ------------- - -Autospeccing is based on the existing `spec` 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 `TypeError` if they are -called incorrectly. - -Before I explain how auto-speccing works, here's why it is needed. - -`Mock` 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 `Mock` api and the other is a more general problem with using -mock objects. - -First the problem specific to `Mock`. `Mock` has two assert methods that are -extremely handy: :meth:`~Mock.assert_called_with` and -:meth:`~Mock.assert_called_once_with`. - - >>> mock = Mock(name='Thing', return_value=None) - >>> mock(1, 2, 3) - >>> mock.assert_called_once_with(1, 2, 3) - >>> mock(1, 2, 3) - >>> mock.assert_called_once_with(1, 2, 3) - Traceback (most recent call last): - ... - AssertionError: Expected to be called once. Called 2 times. - -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: - -.. code-block:: pycon - - >>> mock = Mock(name='Thing', return_value=None) - >>> mock(1, 2, 3) - >>> mock.assret_called_once_with(4, 5, 6) - -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. - -`mock` already provides a feature to help with this, called speccing. If you -use a class or instance as the `spec` for a mock then you can only access -attributes on the mock that exist on the real class: - - >>> from urllib import request - >>> mock = Mock(spec=request.Request) - >>> mock.assret_called_with - Traceback (most recent call last): - ... - AttributeError: Mock object has no attribute 'assret_called_with' - -The spec only applies to the mock itself, so we still have the same issue -with any methods on the mock: - -.. code-block:: pycon - - >>> mock.has_data() - <mock.Mock object at 0x...> - >>> mock.has_data.assret_called_with() - -Auto-speccing solves this problem. You can either pass `autospec=True` to -`patch` / `patch.object` or use the `create_autospec` function to create a -mock with a spec. If you use the `autospec=True` argument to `patch` 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: - - >>> from urllib import request - >>> patcher = patch('__main__.request', autospec=True) - >>> mock_request = patcher.start() - >>> request is mock_request - True - >>> mock_request.Request - <MagicMock name='request.Request' spec='Request' id='...'> - -You can see that `request.Request` has a spec. `request.Request` takes two -arguments in the constructor (one of which is `self`). Here's what happens if -we try to call it incorrectly: - - >>> req = request.Request() - Traceback (most recent call last): - ... - TypeError: <lambda>() takes at least 2 arguments (1 given) - -The spec also applies to instantiated classes (i.e. the return value of -specced mocks): - - >>> req = request.Request('foo') - >>> req - <NonCallableMagicMock name='request.Request()' spec='Request' id='...'> - -`Request` objects are not callable, so the return value of instantiating our -mocked out `request.Request` is a non-callable mock. With the spec in place -any typos in our asserts will raise the correct error: - - >>> req.add_header('spam', 'eggs') - <MagicMock name='request.Request().add_header()' id='...'> - >>> req.add_header.assret_called_with - Traceback (most recent call last): - ... - AttributeError: Mock object has no attribute 'assret_called_with' - >>> req.add_header.assert_called_with('spam', 'eggs') - -In many cases you will just be able to add `autospec=True` to your existing -`patch` calls and then be protected against bugs due to typos and api -changes. - -As well as using `autospec` through `patch` there is a -:func:`create_autospec` for creating autospecced mocks directly: - - >>> from urllib import request - >>> mock_request = create_autospec(request) - >>> mock_request.Request('foo', 'bar') - <NonCallableMagicMock name='mock.Request()' spec='Request' id='...'> - -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 more serious problem is that it is common for instance attributes to be -created in the `__init__` 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. - - >>> class Something(object): - ... def __init__(self): - ... self.a = 33 - ... - >>> with patch('__main__.Something', autospec=True): - ... thing = Something() - ... thing.a - ... - Traceback (most recent call last): - ... - AttributeError: Mock object has no attribute 'a' - -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: - - >>> with patch('__main__.Something', autospec=True): - ... thing = Something() - ... thing.a = 33 - ... - -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: - - >>> with patch('__main__.Something', autospec=True, spec_set=True): - ... thing = Something() - ... thing.a = 33 - ... - Traceback (most recent call last): - ... - AttributeError: Mock object has no attribute 'a' - -Probably the best way of solving the problem is to add class attributes as -default values for instance members initialised in `__init__`. Note that if -you are only setting default attributes in `__init__` then providing them via -class attributes (shared between instances of course) is faster too. e.g. - -.. code-block:: python - - class Something(object): - a = 33 - -This brings up another issue. It is relatively common to provide a default -value of `None` for members that will later be an object of a different type. -`None` would be useless as a spec because it wouldn't let you access *any* -attributes or methods on it. As `None` 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 `None`. These will -just be ordinary mocks (well - `MagicMocks`): - - >>> class Something(object): - ... member = None - ... - >>> mock = create_autospec(Something) - >>> mock.member.foo.bar.baz() - <MagicMock name='mock.member.foo.bar.baz()' id='...'> - -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 `patch` supports this - you can simply pass the -alternative object as the `autospec` argument: - - >>> class Something(object): - ... def __init__(self): - ... self.a = 33 - ... - >>> class SomethingForTest(Something): - ... a = 33 - ... - >>> p = patch('__main__.Something', autospec=SomethingForTest) - >>> mock = p.start() - >>> mock.a - <NonCallableMagicMock name='Something.a' spec='int' id='...'> - - -.. [#] 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 `dir` - that are done. diff --git a/Doc/library/unittest.mock-magicmethods.rst b/Doc/library/unittest.mock-magicmethods.rst deleted file mode 100644 index f5209ab..0000000 --- a/Doc/library/unittest.mock-magicmethods.rst +++ /dev/null @@ -1,226 +0,0 @@ -:mod:`unittest.mock` --- MagicMock and magic method support -=========================================================== - -.. module:: unittest.mock - :synopsis: Mock object library. -.. moduleauthor:: Michael Foord <michael@python.org> -.. currentmodule:: unittest.mock - -.. versionadded:: 3.3 - - -.. _magic-methods: - -Mocking Magic Methods ---------------------- - -:class:`Mock` 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 [#]_, 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 ``self`` as -the first argument [#]_. - - >>> def __str__(self): - ... return 'fooble' - ... - >>> mock = Mock() - >>> mock.__str__ = __str__ - >>> str(mock) - 'fooble' - - >>> mock = Mock() - >>> mock.__str__ = Mock() - >>> mock.__str__.return_value = 'fooble' - >>> str(mock) - 'fooble' - - >>> mock = Mock() - >>> mock.__iter__ = Mock(return_value=iter([])) - >>> list(mock) - [] - -One use case for this is for mocking objects used as context managers in a -`with` statement: - - >>> mock = Mock() - >>> mock.__enter__ = Mock(return_value='foo') - >>> mock.__exit__ = Mock(return_value=False) - >>> with mock as m: - ... assert m == 'foo' - ... - >>> mock.__enter__.assert_called_with() - >>> mock.__exit__.assert_called_with(None, None, None) - -Calls to magic methods do not appear in :attr:`~Mock.method_calls`, but they -are recorded in :attr:`~Mock.mock_calls`. - -.. 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 `AttributeError`. - -The full list of supported magic methods is: - -* ``__hash__``, ``__sizeof__``, ``__repr__`` and ``__str__`` -* ``__dir__``, ``__format__`` and ``__subclasses__`` -* ``__floor__``, ``__trunc__`` and ``__ceil__`` -* Comparisons: ``__cmp__``, ``__lt__``, ``__gt__``, ``__le__``, ``__ge__``, - ``__eq__`` and ``__ne__`` -* Container methods: ``__getitem__``, ``__setitem__``, ``__delitem__``, - ``__contains__``, ``__len__``, ``__iter__``, ``__getslice__``, - ``__setslice__``, ``__reversed__`` and ``__missing__`` -* Context manager: ``__enter__`` and ``__exit__`` -* Unary numeric methods: ``__neg__``, ``__pos__`` and ``__invert__`` -* The numeric methods (including right hand and in-place variants): - ``__add__``, ``__sub__``, ``__mul__``, ``__div__``, - ``__floordiv__``, ``__mod__``, ``__divmod__``, ``__lshift__``, - ``__rshift__``, ``__and__``, ``__xor__``, ``__or__``, and ``__pow__`` -* Numeric conversion methods: ``__complex__``, ``__int__``, ``__float__``, - ``__index__`` and ``__coerce__`` -* Descriptor methods: ``__get__``, ``__set__`` and ``__delete__`` -* Pickling: ``__reduce__``, ``__reduce_ex__``, ``__getinitargs__``, - ``__getnewargs__``, ``__getstate__`` and ``__setstate__`` - - -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: - -* ``__getattr__``, ``__setattr__``, ``__init__`` and ``__new__`` -* ``__prepare__``, ``__instancecheck__``, ``__subclasscheck__``, ``__del__`` - - - -Magic Mock ----------- - -There are two `MagicMock` variants: `MagicMock` and `NonCallableMagicMock`. - - -.. class:: MagicMock(*args, **kw) - - ``MagicMock`` is a subclass of :class:`Mock` with default implementations - of most of the magic methods. You can use ``MagicMock`` without having to - configure the magic methods yourself. - - The constructor parameters have the same meaning as for :class:`Mock`. - - If you use the `spec` or `spec_set` arguments then *only* magic methods - that exist in the spec will be created. - - -.. class:: NonCallableMagicMock(*args, **kw) - - A non-callable version of `MagicMock`. - - The constructor parameters have the same meaning as for - :class:`MagicMock`, with the exception of `return_value` and - `side_effect` which have no meaning on a non-callable mock. - -The magic methods are setup with `MagicMock` objects, so you can configure them -and use them in the usual way: - - >>> mock = MagicMock() - >>> mock[3] = 'fish' - >>> mock.__setitem__.assert_called_with(3, 'fish') - >>> mock.__getitem__.return_value = 'result' - >>> mock[2] - 'result' - -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: - -* ``__lt__``: NotImplemented -* ``__gt__``: NotImplemented -* ``__le__``: NotImplemented -* ``__ge__``: NotImplemented -* ``__int__`` : 1 -* ``__contains__`` : False -* ``__len__`` : 1 -* ``__iter__`` : iter([]) -* ``__exit__`` : False -* ``__complex__`` : 1j -* ``__float__`` : 1.0 -* ``__bool__`` : True -* ``__index__`` : 1 -* ``__hash__`` : default hash for the mock -* ``__str__`` : default str for the mock -* ``__sizeof__``: default sizeof for the mock - -For example: - - >>> mock = MagicMock() - >>> int(mock) - 1 - >>> len(mock) - 0 - >>> list(mock) - [] - >>> object() in mock - False - -The two equality method, `__eq__` and `__ne__`, are special. -They do the default equality comparison on identity, using a side -effect, unless you change their return value to return something else: - - >>> MagicMock() == 3 - False - >>> MagicMock() != 3 - True - >>> mock = MagicMock() - >>> mock.__eq__.return_value = True - >>> mock == 3 - True - -The return value of `MagicMock.__iter__` can be any iterable object and isn't -required to be an iterator: - - >>> mock = MagicMock() - >>> mock.__iter__.return_value = ['a', 'b', 'c'] - >>> list(mock) - ['a', 'b', 'c'] - >>> list(mock) - ['a', 'b', 'c'] - -If the return value *is* an iterator, then iterating over it once will consume -it and subsequent iterations will result in an empty list: - - >>> mock.__iter__.return_value = iter(['a', 'b', 'c']) - >>> list(mock) - ['a', 'b', 'c'] - >>> list(mock) - [] - -``MagicMock`` 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 ``MagicMock`` are: - -* ``__subclasses__`` -* ``__dir__`` -* ``__format__`` -* ``__get__``, ``__set__`` and ``__delete__`` -* ``__reversed__`` and ``__missing__`` -* ``__reduce__``, ``__reduce_ex__``, ``__getinitargs__``, ``__getnewargs__``, - ``__getstate__`` and ``__setstate__`` -* ``__getformat__`` and ``__setformat__`` - - - -.. [#] 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. -.. [#] The function is basically hooked up to the class, but each ``Mock`` - instance is kept isolated from the others. diff --git a/Doc/library/unittest.mock-patch.rst b/Doc/library/unittest.mock-patch.rst deleted file mode 100644 index e3e3525..0000000 --- a/Doc/library/unittest.mock-patch.rst +++ /dev/null @@ -1,538 +0,0 @@ -:mod:`unittest.mock` --- the patchers -===================================== - -.. module:: unittest.mock - :synopsis: Mock object library. -.. moduleauthor:: Michael Foord <michael@python.org> -.. currentmodule:: unittest.mock - -.. versionadded:: 3.3 - -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. - - -patch ------ - -.. note:: - - `patch` is straightforward to use. The key is to do the patching in the - right namespace. See the section `where to patch`_. - -.. function:: patch(target, new=DEFAULT, spec=None, create=False, spec_set=None, autospec=None, new_callable=None, **kwargs) - - `patch` acts as a function decorator, class decorator or a context - manager. Inside the body of the function or with statement, the `target` - (specified in the form `'package.module.ClassName'`) is patched - with a `new` object. When the function/with statement exits the patch is - undone. - - The `target` is imported and the specified attribute patched with the new - object, so it must be importable from the environment you are calling the - decorator from. The target is imported when the decorated function is - executed, not at decoration time. - - If `new` is omitted, then a new `MagicMock` is created and passed in as an - extra argument to the decorated function. - - The `spec` and `spec_set` keyword arguments are passed to the `MagicMock` - if patch is creating one for you. - - In addition you can pass `spec=True` or `spec_set=True`, 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 `MagicMock` is - used. - - A more powerful form of `spec` is `autospec`. If you set `autospec=True` - then the mock with 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 `TypeError` 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 :func:`create_autospec` function and - :ref:`auto-speccing`. - - Instead of `autospec=True` you can pass `autospec=some_object` to use an - arbitrary object as the spec instead of the one being replaced. - - By default `patch` will fail to replace attributes that don't exist. If - you pass in `create=True`, 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 by - default because it can be dangerous. With it switched on you can write - passing tests against APIs that don't actually exist! - - Patch can be used as a `TestCase` 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. `patch` finds - tests by looking for method names that start with `patch.TEST_PREFIX`. - By default this is `test`, which matches the way `unittest` finds tests. - You can specify an alternative prefix by setting `patch.TEST_PREFIX`. - - 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 `patch` is creating a mock object for you. - - `patch` takes arbitrary keyword arguments. These will be passed to - the `Mock` (or `new_callable`) on construction. - - `patch.dict(...)`, `patch.multiple(...)` and `patch.object(...)` are - available for alternate use-cases. - - -Patching a class replaces the class with a `MagicMock` *instance*. If the -class is instantiated in the code under test then it will be the -:attr:`~Mock.return_value` of the mock that will be used. - -If the class is instantiated multiple times you could use -:attr:`~Mock.side_effect` 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 `return_value`. For example: - - >>> class Class(object): - ... def method(self): - ... pass - ... - >>> with patch('__main__.Class') as MockClass: - ... instance = MockClass.return_value - ... instance.method.return_value = 'foo' - ... assert Class() is instance - ... assert Class().method() == 'foo' - ... - -If you use `spec` or `spec_set` and `patch` is replacing a *class*, then the -return value of the created mock will have the same spec. - - >>> Original = Class - >>> patcher = patch('__main__.Class', spec=True) - >>> MockClass = patcher.start() - >>> instance = MockClass() - >>> assert isinstance(instance, Original) - >>> patcher.stop() - -The `new_callable` argument is useful where you want to use an alternative -class to the default :class:`MagicMock` for the created mock. For example, if -you wanted a :class:`NonCallableMock` to be used: - - >>> thing = object() - >>> with patch('__main__.thing', new_callable=NonCallableMock) as mock_thing: - ... assert thing is mock_thing - ... thing() - ... - Traceback (most recent call last): - ... - TypeError: 'NonCallableMock' object is not callable - -Another use case might be to replace an object with a `StringIO` instance: - - >>> from StringIO import StringIO - >>> def foo(): - ... print 'Something' - ... - >>> @patch('sys.stdout', new_callable=StringIO) - ... def test(mock_stdout): - ... foo() - ... assert mock_stdout.getvalue() == 'Something\n' - ... - >>> test() - -When `patch` 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: - - >>> patcher = patch('__main__.thing', first='one', second='two') - >>> mock_thing = patcher.start() - >>> mock_thing.first - 'one' - >>> mock_thing.second - 'two' - -As well as attributes on the created mock attributes, like the -:attr:`~Mock.return_value` and :attr:`~Mock.side_effect`, 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 `patch` call using `**`: - - >>> config = {'method.return_value': 3, 'other.side_effect': KeyError} - >>> patcher = patch('__main__.thing', **config) - >>> mock_thing = patcher.start() - >>> mock_thing.method() - 3 - >>> mock_thing.other() - Traceback (most recent call last): - ... - KeyError - - -patch.object ------------- - -.. function:: patch.object(target, attribute, new=DEFAULT, spec=None, create=False, spec_set=None, autospec=None, new_callable=None, **kwargs) - - patch the named member (`attribute`) on an object (`target`) with a mock - object. - - `patch.object` 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 `patch`. Like `patch`, - `patch.object` takes arbitrary keyword arguments for configuring the mock - object it creates. - - When used as a class decorator `patch.object` honours `patch.TEST_PREFIX` - for choosing which methods to wrap. - -You can either call `patch.object` 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: - - >>> @patch.object(SomeClass, 'class_method') - ... def test(mock_method): - ... SomeClass.class_method(3) - ... mock_method.assert_called_with(3) - ... - >>> test() - -`spec`, `create` and the other arguments to `patch.object` have the same -meaning as they do for `patch`. - - -patch.dict ----------- - -.. function:: patch.dict(in_dict, values=(), clear=False, **kwargs) - - 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 `(key, value)` pairs. - - If `clear` is True then the dictionary will be cleared before the new - values are set. - - `patch.dict` can also be called with arbitrary keyword arguments to set - values in the dictionary. - - `patch.dict` can be used as a context manager, decorator or class - decorator. When used as a class decorator `patch.dict` honours - `patch.TEST_PREFIX` for choosing which methods to wrap. - -`patch.dict` 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. - - >>> foo = {} - >>> with patch.dict(foo, {'newkey': 'newvalue'}): - ... assert foo == {'newkey': 'newvalue'} - ... - >>> assert foo == {} - - >>> import os - >>> with patch.dict('os.environ', {'newkey': 'newvalue'}): - ... print os.environ['newkey'] - ... - newvalue - >>> assert 'newkey' not in os.environ - -Keywords can be used in the `patch.dict` call to set values in the dictionary: - - >>> mymodule = MagicMock() - >>> mymodule.function.return_value = 'fish' - >>> with patch.dict('sys.modules', mymodule=mymodule): - ... import mymodule - ... mymodule.function('some', 'args') - ... - 'fish' - -`patch.dict` 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 `__getitem__`, `__setitem__`, `__delitem__` and either -`__iter__` or `__contains__`. - - >>> class Container(object): - ... 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) - ... - >>> thing = Container() - >>> thing['one'] = 1 - >>> with patch.dict(thing, one=2, two=3): - ... assert thing['one'] == 2 - ... assert thing['two'] == 3 - ... - >>> assert thing['one'] == 1 - >>> assert list(thing) == ['one'] - - -patch.multiple --------------- - -.. function:: patch.multiple(target, spec=None, create=False, spec_set=None, autospec=None, new_callable=None, **kwargs) - - 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:: - - with patch.multiple(settings, FIRST_PATCH='one', SECOND_PATCH='two'): - ... - - Use :data:`DEFAULT` as the value if you want `patch.multiple` 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 `patch.multiple` is - used as a context manager. - - `patch.multiple` 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 `patch`. These arguments will - be applied to *all* patches done by `patch.multiple`. - - When used as a class decorator `patch.multiple` honours `patch.TEST_PREFIX` - for choosing which methods to wrap. - -If you want `patch.multiple` to create mocks for you, then you can use -:data:`DEFAULT` as the value. If you use `patch.multiple` as a decorator -then the created mocks are passed into the decorated function by keyword. - - >>> thing = object() - >>> other = object() - - >>> @patch.multiple('__main__', thing=DEFAULT, other=DEFAULT) - ... def test_function(thing, other): - ... assert isinstance(thing, MagicMock) - ... assert isinstance(other, MagicMock) - ... - >>> test_function() - -`patch.multiple` can be nested with other `patch` decorators, but put arguments -passed by keyword *after* any of the standard arguments created by `patch`: - - >>> @patch('sys.exit') - ... @patch.multiple('__main__', thing=DEFAULT, other=DEFAULT) - ... def test_function(mock_exit, other, thing): - ... assert 'other' in repr(other) - ... assert 'thing' in repr(thing) - ... assert 'exit' in repr(mock_exit) - ... - >>> test_function() - -If `patch.multiple` is used as a context manager, the value returned by the -context manger is a dictionary where created mocks are keyed by name: - - >>> with patch.multiple('__main__', thing=DEFAULT, other=DEFAULT) as values: - ... assert 'other' in repr(values['other']) - ... assert 'thing' in repr(values['thing']) - ... assert values['thing'] is thing - ... assert values['other'] is other - ... - - -.. _start-and-stop: - -patch methods: start and stop ------------------------------ - -All the patchers have `start` and `stop` methods. These make it simpler to do -patching in `setUp` methods or where you want to do multiple patches without -nesting decorators or with statements. - -To use them call `patch`, `patch.object` or `patch.dict` as normal and keep a -reference to the returned `patcher` object. You can then call `start` to put -the patch in place and `stop` to undo it. - -If you are using `patch` to create a mock for you then it will be returned by -the call to `patcher.start`. - - >>> patcher = patch('package.module.ClassName') - >>> from package import module - >>> original = module.ClassName - >>> new_mock = patcher.start() - >>> assert module.ClassName is not original - >>> assert module.ClassName is new_mock - >>> patcher.stop() - >>> assert module.ClassName is original - >>> assert module.ClassName is not new_mock - - -A typical use case for this might be for doing multiple patches in the `setUp` -method of a `TestCase`: - - >>> class MyTest(TestCase): - ... def setUp(self): - ... self.patcher1 = patch('package.module.Class1') - ... self.patcher2 = patch('package.module.Class2') - ... 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 - ... - >>> MyTest('test_something').run() - -.. caution:: - - If you use this technique you must ensure that the patching is "undone" by - calling `stop`. This can be fiddlier than you might think, because if an - exception is raised in the ``setUp`` then ``tearDown`` is not called. - :meth:`unittest.TestCase.addCleanup` makes this easier: - - >>> class MyTest(TestCase): - ... def setUp(self): - ... patcher = patch('package.module.Class') - ... self.MockClass = patcher.start() - ... self.addCleanup(patcher.stop) - ... - ... def test_something(self): - ... assert package.module.Class is self.MockClass - ... - - As an added bonus you no longer need to keep a reference to the `patcher` - object. - -In fact `start` and `stop` are just aliases for the context manager -`__enter__` and `__exit__` methods. - - -TEST_PREFIX ------------ - -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 `test` as being test methods. This is the same way that the -:class:`unittest.TestLoader` 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 `patch.TEST_PREFIX`: - - >>> patch.TEST_PREFIX = 'foo' - >>> value = 3 - >>> - >>> @patch('__main__.value', 'not three') - ... class Thing(object): - ... def foo_one(self): - ... print value - ... def foo_two(self): - ... print value - ... - >>> - >>> Thing().foo_one() - not three - >>> Thing().foo_two() - not three - >>> value - 3 - - -Nesting Patch Decorators ------------------------- - -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: - - >>> @patch.object(SomeClass, 'class_method') - ... @patch.object(SomeClass, 'static_method') - ... def test(mock1, mock2): - ... assert SomeClass.static_method is mock1 - ... assert SomeClass.class_method is mock2 - ... SomeClass.static_method('foo') - ... SomeClass.class_method('bar') - ... return mock1, mock2 - ... - >>> mock1, mock2 = test() - >>> mock1.assert_called_once_with('foo') - >>> mock2.assert_called_once_with('bar') - - -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. - - -.. _where-to-patch: - -Where to patch --------------- - -`patch` 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:: - - a.py - -> Defines SomeClass - - b.py - -> from a import SomeClass - -> some_function instantiates SomeClass - -Now we want to test `some_function` but we want to mock out `SomeClass` using -`patch`. The problem is that when we import module b, which we will have to -do then it imports `SomeClass` from module a. If we use `patch` to mock out -`a.SomeClass` then it will have no effect on our test; module b already has a -reference to the *real* `SomeClass` and it looks like our patching had no -effect. - -The key is to patch out `SomeClass` where it is used (or where it is looked up -). In this case `some_function` will actually look up `SomeClass` in module b, -where we have imported it. The patching should look like:: - - @patch('b.SomeClass') - -However, consider the alternative scenario where instead of `from a import -SomeClass` module b does `import a` and `some_function` uses `a.SomeClass`. Both -of these import forms are common. In this case the class we want to patch is -being looked up on the a module and so we have to patch `a.SomeClass` instead:: - - @patch('a.SomeClass') - - -Patching Descriptors and Proxy Objects --------------------------------------- - -Both patch_ and patch.object_ 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 `django setttings object -<http://www.voidspace.org.uk/python/weblog/arch_d7_2010_12_04.shtml#e1198>`_. diff --git a/Doc/library/unittest.mock.rst b/Doc/library/unittest.mock.rst index 71b7386..3e5f9fa 100644 --- a/Doc/library/unittest.mock.rst +++ b/Doc/library/unittest.mock.rst @@ -84,7 +84,6 @@ mock (or other object) during the test and restored when the test ends: ... def test(MockClass1, MockClass2): ... module.ClassName1() ... module.ClassName2() - ... assert MockClass1 is module.ClassName1 ... assert MockClass2 is module.ClassName2 ... assert MockClass1.called @@ -898,3 +897,1287 @@ method: 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 :ref:`magic methods <magic-methods>`. + + +The patchers +============ + +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. + + +patch +----- + +.. note:: + + `patch` is straightforward to use. The key is to do the patching in the + right namespace. See the section `where to patch`_. + +.. function:: patch(target, new=DEFAULT, spec=None, create=False, spec_set=None, autospec=None, new_callable=None, **kwargs) + + `patch` acts as a function decorator, class decorator or a context + manager. Inside the body of the function or with statement, the `target` + (specified in the form `'package.module.ClassName'`) is patched + with a `new` object. When the function/with statement exits the patch is + undone. + + The `target` is imported and the specified attribute patched with the new + object, so it must be importable from the environment you are calling the + decorator from. The target is imported when the decorated function is + executed, not at decoration time. + + If `new` is omitted, then a new `MagicMock` is created and passed in as an + extra argument to the decorated function. + + The `spec` and `spec_set` keyword arguments are passed to the `MagicMock` + if patch is creating one for you. + + In addition you can pass `spec=True` or `spec_set=True`, 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 `MagicMock` is + used. + + A more powerful form of `spec` is `autospec`. If you set `autospec=True` + then the mock with 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 `TypeError` 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 :func:`create_autospec` function and + :ref:`auto-speccing`. + + Instead of `autospec=True` you can pass `autospec=some_object` to use an + arbitrary object as the spec instead of the one being replaced. + + By default `patch` will fail to replace attributes that don't exist. If + you pass in `create=True`, 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 by + default because it can be dangerous. With it switched on you can write + passing tests against APIs that don't actually exist! + + Patch can be used as a `TestCase` 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. `patch` finds + tests by looking for method names that start with `patch.TEST_PREFIX`. + By default this is `test`, which matches the way `unittest` finds tests. + You can specify an alternative prefix by setting `patch.TEST_PREFIX`. + + 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 `patch` is creating a mock object for you. + + `patch` takes arbitrary keyword arguments. These will be passed to + the `Mock` (or `new_callable`) on construction. + + `patch.dict(...)`, `patch.multiple(...)` and `patch.object(...)` are + available for alternate use-cases. + + +Patching a class replaces the class with a `MagicMock` *instance*. If the +class is instantiated in the code under test then it will be the +:attr:`~Mock.return_value` of the mock that will be used. + +If the class is instantiated multiple times you could use +:attr:`~Mock.side_effect` 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 `return_value`. For example: + + >>> class Class(object): + ... def method(self): + ... pass + ... + >>> with patch('__main__.Class') as MockClass: + ... instance = MockClass.return_value + ... instance.method.return_value = 'foo' + ... assert Class() is instance + ... assert Class().method() == 'foo' + ... + +If you use `spec` or `spec_set` and `patch` is replacing a *class*, then the +return value of the created mock will have the same spec. + + >>> Original = Class + >>> patcher = patch('__main__.Class', spec=True) + >>> MockClass = patcher.start() + >>> instance = MockClass() + >>> assert isinstance(instance, Original) + >>> patcher.stop() + +The `new_callable` argument is useful where you want to use an alternative +class to the default :class:`MagicMock` for the created mock. For example, if +you wanted a :class:`NonCallableMock` to be used: + + >>> thing = object() + >>> with patch('__main__.thing', new_callable=NonCallableMock) as mock_thing: + ... assert thing is mock_thing + ... thing() + ... + Traceback (most recent call last): + ... + TypeError: 'NonCallableMock' object is not callable + +Another use case might be to replace an object with a `StringIO` instance: + + >>> from StringIO import StringIO + >>> def foo(): + ... print 'Something' + ... + >>> @patch('sys.stdout', new_callable=StringIO) + ... def test(mock_stdout): + ... foo() + ... assert mock_stdout.getvalue() == 'Something\n' + ... + >>> test() + +When `patch` 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: + + >>> patcher = patch('__main__.thing', first='one', second='two') + >>> mock_thing = patcher.start() + >>> mock_thing.first + 'one' + >>> mock_thing.second + 'two' + +As well as attributes on the created mock attributes, like the +:attr:`~Mock.return_value` and :attr:`~Mock.side_effect`, 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 `patch` call using `**`: + + >>> config = {'method.return_value': 3, 'other.side_effect': KeyError} + >>> patcher = patch('__main__.thing', **config) + >>> mock_thing = patcher.start() + >>> mock_thing.method() + 3 + >>> mock_thing.other() + Traceback (most recent call last): + ... + KeyError + + +patch.object +------------ + +.. function:: patch.object(target, attribute, new=DEFAULT, spec=None, create=False, spec_set=None, autospec=None, new_callable=None, **kwargs) + + patch the named member (`attribute`) on an object (`target`) with a mock + object. + + `patch.object` 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 `patch`. Like `patch`, + `patch.object` takes arbitrary keyword arguments for configuring the mock + object it creates. + + When used as a class decorator `patch.object` honours `patch.TEST_PREFIX` + for choosing which methods to wrap. + +You can either call `patch.object` 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: + + >>> @patch.object(SomeClass, 'class_method') + ... def test(mock_method): + ... SomeClass.class_method(3) + ... mock_method.assert_called_with(3) + ... + >>> test() + +`spec`, `create` and the other arguments to `patch.object` have the same +meaning as they do for `patch`. + + +patch.dict +---------- + +.. function:: patch.dict(in_dict, values=(), clear=False, **kwargs) + + 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 `(key, value)` pairs. + + If `clear` is True then the dictionary will be cleared before the new + values are set. + + `patch.dict` can also be called with arbitrary keyword arguments to set + values in the dictionary. + + `patch.dict` can be used as a context manager, decorator or class + decorator. When used as a class decorator `patch.dict` honours + `patch.TEST_PREFIX` for choosing which methods to wrap. + +`patch.dict` 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. + + >>> foo = {} + >>> with patch.dict(foo, {'newkey': 'newvalue'}): + ... assert foo == {'newkey': 'newvalue'} + ... + >>> assert foo == {} + + >>> import os + >>> with patch.dict('os.environ', {'newkey': 'newvalue'}): + ... print os.environ['newkey'] + ... + newvalue + >>> assert 'newkey' not in os.environ + +Keywords can be used in the `patch.dict` call to set values in the dictionary: + + >>> mymodule = MagicMock() + >>> mymodule.function.return_value = 'fish' + >>> with patch.dict('sys.modules', mymodule=mymodule): + ... import mymodule + ... mymodule.function('some', 'args') + ... + 'fish' + +`patch.dict` 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 `__getitem__`, `__setitem__`, `__delitem__` and either +`__iter__` or `__contains__`. + + >>> class Container(object): + ... 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) + ... + >>> thing = Container() + >>> thing['one'] = 1 + >>> with patch.dict(thing, one=2, two=3): + ... assert thing['one'] == 2 + ... assert thing['two'] == 3 + ... + >>> assert thing['one'] == 1 + >>> assert list(thing) == ['one'] + + +patch.multiple +-------------- + +.. function:: patch.multiple(target, spec=None, create=False, spec_set=None, autospec=None, new_callable=None, **kwargs) + + 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:: + + with patch.multiple(settings, FIRST_PATCH='one', SECOND_PATCH='two'): + ... + + Use :data:`DEFAULT` as the value if you want `patch.multiple` 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 `patch.multiple` is + used as a context manager. + + `patch.multiple` 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 `patch`. These arguments will + be applied to *all* patches done by `patch.multiple`. + + When used as a class decorator `patch.multiple` honours `patch.TEST_PREFIX` + for choosing which methods to wrap. + +If you want `patch.multiple` to create mocks for you, then you can use +:data:`DEFAULT` as the value. If you use `patch.multiple` as a decorator +then the created mocks are passed into the decorated function by keyword. + + >>> thing = object() + >>> other = object() + + >>> @patch.multiple('__main__', thing=DEFAULT, other=DEFAULT) + ... def test_function(thing, other): + ... assert isinstance(thing, MagicMock) + ... assert isinstance(other, MagicMock) + ... + >>> test_function() + +`patch.multiple` can be nested with other `patch` decorators, but put arguments +passed by keyword *after* any of the standard arguments created by `patch`: + + >>> @patch('sys.exit') + ... @patch.multiple('__main__', thing=DEFAULT, other=DEFAULT) + ... def test_function(mock_exit, other, thing): + ... assert 'other' in repr(other) + ... assert 'thing' in repr(thing) + ... assert 'exit' in repr(mock_exit) + ... + >>> test_function() + +If `patch.multiple` is used as a context manager, the value returned by the +context manger is a dictionary where created mocks are keyed by name: + + >>> with patch.multiple('__main__', thing=DEFAULT, other=DEFAULT) as values: + ... assert 'other' in repr(values['other']) + ... assert 'thing' in repr(values['thing']) + ... assert values['thing'] is thing + ... assert values['other'] is other + ... + + +.. _start-and-stop: + +patch methods: start and stop +----------------------------- + +All the patchers have `start` and `stop` methods. These make it simpler to do +patching in `setUp` methods or where you want to do multiple patches without +nesting decorators or with statements. + +To use them call `patch`, `patch.object` or `patch.dict` as normal and keep a +reference to the returned `patcher` object. You can then call `start` to put +the patch in place and `stop` to undo it. + +If you are using `patch` to create a mock for you then it will be returned by +the call to `patcher.start`. + + >>> patcher = patch('package.module.ClassName') + >>> from package import module + >>> original = module.ClassName + >>> new_mock = patcher.start() + >>> assert module.ClassName is not original + >>> assert module.ClassName is new_mock + >>> patcher.stop() + >>> assert module.ClassName is original + >>> assert module.ClassName is not new_mock + + +A typical use case for this might be for doing multiple patches in the `setUp` +method of a `TestCase`: + + >>> class MyTest(TestCase): + ... def setUp(self): + ... self.patcher1 = patch('package.module.Class1') + ... self.patcher2 = patch('package.module.Class2') + ... 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 + ... + >>> MyTest('test_something').run() + +.. caution:: + + If you use this technique you must ensure that the patching is "undone" by + calling `stop`. This can be fiddlier than you might think, because if an + exception is raised in the ``setUp`` then ``tearDown`` is not called. + :meth:`unittest.TestCase.addCleanup` makes this easier: + + >>> class MyTest(TestCase): + ... def setUp(self): + ... patcher = patch('package.module.Class') + ... self.MockClass = patcher.start() + ... self.addCleanup(patcher.stop) + ... + ... def test_something(self): + ... assert package.module.Class is self.MockClass + ... + + As an added bonus you no longer need to keep a reference to the `patcher` + object. + +In fact `start` and `stop` are just aliases for the context manager +`__enter__` and `__exit__` methods. + + +TEST_PREFIX +----------- + +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 `test` as being test methods. This is the same way that the +:class:`unittest.TestLoader` 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 `patch.TEST_PREFIX`: + + >>> patch.TEST_PREFIX = 'foo' + >>> value = 3 + >>> + >>> @patch('__main__.value', 'not three') + ... class Thing(object): + ... def foo_one(self): + ... print value + ... def foo_two(self): + ... print value + ... + >>> + >>> Thing().foo_one() + not three + >>> Thing().foo_two() + not three + >>> value + 3 + + +Nesting Patch Decorators +------------------------ + +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: + + >>> @patch.object(SomeClass, 'class_method') + ... @patch.object(SomeClass, 'static_method') + ... def test(mock1, mock2): + ... assert SomeClass.static_method is mock1 + ... assert SomeClass.class_method is mock2 + ... SomeClass.static_method('foo') + ... SomeClass.class_method('bar') + ... return mock1, mock2 + ... + >>> mock1, mock2 = test() + >>> mock1.assert_called_once_with('foo') + >>> mock2.assert_called_once_with('bar') + + +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. + + +.. _where-to-patch: + +Where to patch +-------------- + +`patch` 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:: + + a.py + -> Defines SomeClass + + b.py + -> from a import SomeClass + -> some_function instantiates SomeClass + +Now we want to test `some_function` but we want to mock out `SomeClass` using +`patch`. The problem is that when we import module b, which we will have to +do then it imports `SomeClass` from module a. If we use `patch` to mock out +`a.SomeClass` then it will have no effect on our test; module b already has a +reference to the *real* `SomeClass` and it looks like our patching had no +effect. + +The key is to patch out `SomeClass` where it is used (or where it is looked up +). In this case `some_function` will actually look up `SomeClass` in module b, +where we have imported it. The patching should look like:: + + @patch('b.SomeClass') + +However, consider the alternative scenario where instead of `from a import +SomeClass` module b does `import a` and `some_function` uses `a.SomeClass`. Both +of these import forms are common. In this case the class we want to patch is +being looked up on the a module and so we have to patch `a.SomeClass` instead:: + + @patch('a.SomeClass') + + +Patching Descriptors and Proxy Objects +-------------------------------------- + +Both patch_ and patch.object_ 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 `django setttings object +<http://www.voidspace.org.uk/python/weblog/arch_d7_2010_12_04.shtml#e1198>`_. + + +Helpers +======= + +sentinel +-------- + +.. data:: sentinel + + The ``sentinel`` 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. + +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. `sentinel` provides a convenient way of +creating and testing the identity of objects like this. + +In this example we monkey patch `method` to return `sentinel.some_object`: + + >>> real = ProductionClass() + >>> real.method = Mock(name="method") + >>> real.method.return_value = sentinel.some_object + >>> result = real.method() + >>> assert result is sentinel.some_object + >>> sentinel.some_object + sentinel.some_object + + +DEFAULT +------- + + +.. data:: DEFAULT + + The `DEFAULT` object is a pre-created sentinel (actually + `sentinel.DEFAULT`). It can be used by :attr:`~Mock.side_effect` + functions to indicate that the normal return value should be used. + + + +call +---- + +.. function:: call(*args, **kwargs) + + `call` is a helper object for making simpler assertions, for comparing + with :attr:`~Mock.call_args`, :attr:`~Mock.call_args_list`, + :attr:`~Mock.mock_calls` and:attr: `~Mock.method_calls`. `call` can also be + used with :meth:`~Mock.assert_has_calls`. + + >>> m = MagicMock(return_value=None) + >>> m(1, 2, a='foo', b='bar') + >>> m() + >>> m.call_args_list == [call(1, 2, a='foo', b='bar'), call()] + True + +.. method:: call.call_list() + + For a call object that represents multiple calls, `call_list` + returns a list of all the intermediate calls as well as the + final call. + +`call_list` 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 :attr:`~Mock.mock_calls` on a mock. Manually constructing +the sequence of calls can be tedious. + +:meth:`~call.call_list` can construct the sequence of calls from the same +chained call: + + >>> m = MagicMock() + >>> m(1).method(arg='foo').other('bar')(2.0) + <MagicMock name='mock().method().other()()' id='...'> + >>> kall = call(1).method(arg='foo').other('bar')(2.0) + >>> kall.call_list() + [call(1), + call().method(arg='foo'), + call().method().other('bar'), + call().method().other()(2.0)] + >>> m.mock_calls == kall.call_list() + True + +.. _calls-as-tuples: + +A `call` 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 `call` +objects that are in the :attr:`Mock.call_args`, :attr:`Mock.call_args_list` and +:attr:`Mock.mock_calls` attributes can be introspected to get at the individual +arguments they contain. + +The `call` objects in :attr:`Mock.call_args` and :attr:`Mock.call_args_list` +are two-tuples of (positional args, keyword args) whereas the `call` objects +in :attr:`Mock.mock_calls`, 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: + + >>> m = MagicMock(return_value=None) + >>> m(1, 2, 3, arg='one', arg2='two') + >>> kall = m.call_args + >>> args, kwargs = kall + >>> args + (1, 2, 3) + >>> kwargs + {'arg2': 'two', 'arg': 'one'} + >>> args is kall[0] + True + >>> kwargs is kall[1] + True + + >>> m = MagicMock() + >>> m.foo(4, 5, 6, arg='two', arg2='three') + <MagicMock name='mock.foo()' id='...'> + >>> kall = m.mock_calls[0] + >>> name, args, kwargs = kall + >>> name + 'foo' + >>> args + (4, 5, 6) + >>> kwargs + {'arg2': 'three', 'arg': 'two'} + >>> name is m.mock_calls[0][0] + True + + +create_autospec +--------------- + +.. function:: create_autospec(spec, spec_set=False, instance=False, **kwargs) + + 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 `True` then attempting to set attributes that don't exist + on the spec object will raise an `AttributeError`. + + 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 `instance=True`. The returned mock + will only be callable if instances of the mock are callable. + + `create_autospec` also takes arbitrary keyword arguments that are passed to + the constructor of the created mock. + +See :ref:`auto-speccing` for examples of how to use auto-speccing with +`create_autospec` and the `autospec` argument to :func:`patch`. + + +ANY +--- + +.. data:: ANY + +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 :attr:`~Mock.call_args` and make more complex +assertions on them. + +To ignore certain arguments you can pass in objects that compare equal to +*everything*. Calls to :meth:`~Mock.assert_called_with` and +:meth:`~Mock.assert_called_once_with` will then succeed no matter what was +passed in. + + >>> mock = Mock(return_value=None) + >>> mock('foo', bar=object()) + >>> mock.assert_called_once_with('foo', bar=ANY) + +`ANY` can also be used in comparisons with call lists like +:attr:`~Mock.mock_calls`: + + >>> m = MagicMock(return_value=None) + >>> m(1) + >>> m(1, 2) + >>> m(object()) + >>> m.mock_calls == [call(1), call(1, 2), ANY] + True + + + +FILTER_DIR +---------- + +.. data:: FILTER_DIR + +`FILTER_DIR` is a module level variable that controls the way mock objects +respond to `dir` (only for Python 2.6 or more recent). The default is `True`, +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 `mock.FILTER_DIR = False`. + +With filtering on, `dir(some_mock)` 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: + + >>> dir(Mock()) + ['assert_any_call', + 'assert_called_once_with', + 'assert_called_with', + 'assert_has_calls', + 'attach_mock', + ... + >>> from urllib import request + >>> dir(Mock(spec=request)) + ['AbstractBasicAuthHandler', + 'AbstractDigestAuthHandler', + 'AbstractHTTPHandler', + 'BaseHandler', + ... + +Many of the not-very-useful (private to `Mock` rather than the thing being +mocked) underscore and double underscore prefixed attributes have been +filtered from the result of calling `dir` on a `Mock`. If you dislike this +behaviour you can switch it off by setting the module level switch +`FILTER_DIR`: + + >>> from unittest import mock + >>> mock.FILTER_DIR = False + >>> dir(mock.Mock()) + ['_NonCallableMock__get_return_value', + '_NonCallableMock__get_side_effect', + '_NonCallableMock__return_value_doc', + '_NonCallableMock__set_return_value', + '_NonCallableMock__set_side_effect', + '__call__', + '__class__', + ... + +Alternatively you can just use `vars(my_mock)` (instance members) and +`dir(type(my_mock))` (type members) to bypass the filtering irrespective of +`mock.FILTER_DIR`. + + +mock_open +--------- + +.. function:: mock_open(mock=None, read_data=None) + + A helper function to create a mock to replace the use of `open`. It works + for `open` called directly or used as a context manager. + + The `mock` argument is the mock object to configure. If `None` (the + default) then a `MagicMock` 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 `read` method of the file handle to return. + This is an empty string by default. + +Using `open` as a context manager is a great way to ensure your file handles +are closed properly and is becoming common:: + + with open('/some/path', 'w') as f: + f.write('something') + +The issue is that even if you mock out the call to `open` it is the +*returned object* that is used as a context manager (and has `__enter__` and +`__exit__` called). + +Mocking context managers with a :class:`MagicMock` is common enough and fiddly +enough that a helper function is useful. + + >>> m = mock_open() + >>> with patch('__main__.open', m, create=True): + ... with open('foo', 'w') as h: + ... h.write('some stuff') + ... + >>> m.mock_calls + [call('foo', 'w'), + call().__enter__(), + call().write('some stuff'), + call().__exit__(None, None, None)] + >>> m.assert_called_once_with('foo', 'w') + >>> handle = m() + >>> handle.write.assert_called_once_with('some stuff') + +And for reading files: + + >>> with patch('__main__.open', mock_open(read_data='bibble'), create=True) as m: + ... with open('foo') as h: + ... result = h.read() + ... + >>> m.assert_called_once_with('foo') + >>> assert result == 'bibble' + + +.. _auto-speccing: + +Autospeccing +------------ + +Autospeccing is based on the existing `spec` 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 `TypeError` if they are +called incorrectly. + +Before I explain how auto-speccing works, here's why it is needed. + +`Mock` 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 `Mock` api and the other is a more general problem with using +mock objects. + +First the problem specific to `Mock`. `Mock` has two assert methods that are +extremely handy: :meth:`~Mock.assert_called_with` and +:meth:`~Mock.assert_called_once_with`. + + >>> mock = Mock(name='Thing', return_value=None) + >>> mock(1, 2, 3) + >>> mock.assert_called_once_with(1, 2, 3) + >>> mock(1, 2, 3) + >>> mock.assert_called_once_with(1, 2, 3) + Traceback (most recent call last): + ... + AssertionError: Expected to be called once. Called 2 times. + +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: + +.. code-block:: pycon + + >>> mock = Mock(name='Thing', return_value=None) + >>> mock(1, 2, 3) + >>> mock.assret_called_once_with(4, 5, 6) + +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. + +`mock` already provides a feature to help with this, called speccing. If you +use a class or instance as the `spec` for a mock then you can only access +attributes on the mock that exist on the real class: + + >>> from urllib import request + >>> mock = Mock(spec=request.Request) + >>> mock.assret_called_with + Traceback (most recent call last): + ... + AttributeError: Mock object has no attribute 'assret_called_with' + +The spec only applies to the mock itself, so we still have the same issue +with any methods on the mock: + +.. code-block:: pycon + + >>> mock.has_data() + <mock.Mock object at 0x...> + >>> mock.has_data.assret_called_with() + +Auto-speccing solves this problem. You can either pass `autospec=True` to +`patch` / `patch.object` or use the `create_autospec` function to create a +mock with a spec. If you use the `autospec=True` argument to `patch` 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: + + >>> from urllib import request + >>> patcher = patch('__main__.request', autospec=True) + >>> mock_request = patcher.start() + >>> request is mock_request + True + >>> mock_request.Request + <MagicMock name='request.Request' spec='Request' id='...'> + +You can see that `request.Request` has a spec. `request.Request` takes two +arguments in the constructor (one of which is `self`). Here's what happens if +we try to call it incorrectly: + + >>> req = request.Request() + Traceback (most recent call last): + ... + TypeError: <lambda>() takes at least 2 arguments (1 given) + +The spec also applies to instantiated classes (i.e. the return value of +specced mocks): + + >>> req = request.Request('foo') + >>> req + <NonCallableMagicMock name='request.Request()' spec='Request' id='...'> + +`Request` objects are not callable, so the return value of instantiating our +mocked out `request.Request` is a non-callable mock. With the spec in place +any typos in our asserts will raise the correct error: + + >>> req.add_header('spam', 'eggs') + <MagicMock name='request.Request().add_header()' id='...'> + >>> req.add_header.assret_called_with + Traceback (most recent call last): + ... + AttributeError: Mock object has no attribute 'assret_called_with' + >>> req.add_header.assert_called_with('spam', 'eggs') + +In many cases you will just be able to add `autospec=True` to your existing +`patch` calls and then be protected against bugs due to typos and api +changes. + +As well as using `autospec` through `patch` there is a +:func:`create_autospec` for creating autospecced mocks directly: + + >>> from urllib import request + >>> mock_request = create_autospec(request) + >>> mock_request.Request('foo', 'bar') + <NonCallableMagicMock name='mock.Request()' spec='Request' id='...'> + +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 more serious problem is that it is common for instance attributes to be +created in the `__init__` 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. + + >>> class Something(object): + ... def __init__(self): + ... self.a = 33 + ... + >>> with patch('__main__.Something', autospec=True): + ... thing = Something() + ... thing.a + ... + Traceback (most recent call last): + ... + AttributeError: Mock object has no attribute 'a' + +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: + + >>> with patch('__main__.Something', autospec=True): + ... thing = Something() + ... thing.a = 33 + ... + +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: + + >>> with patch('__main__.Something', autospec=True, spec_set=True): + ... thing = Something() + ... thing.a = 33 + ... + Traceback (most recent call last): + ... + AttributeError: Mock object has no attribute 'a' + +Probably the best way of solving the problem is to add class attributes as +default values for instance members initialised in `__init__`. Note that if +you are only setting default attributes in `__init__` then providing them via +class attributes (shared between instances of course) is faster too. e.g. + +.. code-block:: python + + class Something(object): + a = 33 + +This brings up another issue. It is relatively common to provide a default +value of `None` for members that will later be an object of a different type. +`None` would be useless as a spec because it wouldn't let you access *any* +attributes or methods on it. As `None` 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 `None`. These will +just be ordinary mocks (well - `MagicMocks`): + + >>> class Something(object): + ... member = None + ... + >>> mock = create_autospec(Something) + >>> mock.member.foo.bar.baz() + <MagicMock name='mock.member.foo.bar.baz()' id='...'> + +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 `patch` supports this - you can simply pass the +alternative object as the `autospec` argument: + + >>> class Something(object): + ... def __init__(self): + ... self.a = 33 + ... + >>> class SomethingForTest(Something): + ... a = 33 + ... + >>> p = patch('__main__.Something', autospec=SomethingForTest) + >>> mock = p.start() + >>> mock.a + <NonCallableMagicMock name='Something.a' spec='int' id='...'> + + +.. [#] 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 `dir` - that are done. + + +MagicMock and magic method support +================================== + +.. _magic-methods: + +Mocking Magic Methods +--------------------- + +:class:`Mock` 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 [#]_, 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 ``self`` as +the first argument [#]_. + + >>> def __str__(self): + ... return 'fooble' + ... + >>> mock = Mock() + >>> mock.__str__ = __str__ + >>> str(mock) + 'fooble' + + >>> mock = Mock() + >>> mock.__str__ = Mock() + >>> mock.__str__.return_value = 'fooble' + >>> str(mock) + 'fooble' + + >>> mock = Mock() + >>> mock.__iter__ = Mock(return_value=iter([])) + >>> list(mock) + [] + +One use case for this is for mocking objects used as context managers in a +`with` statement: + + >>> mock = Mock() + >>> mock.__enter__ = Mock(return_value='foo') + >>> mock.__exit__ = Mock(return_value=False) + >>> with mock as m: + ... assert m == 'foo' + ... + >>> mock.__enter__.assert_called_with() + >>> mock.__exit__.assert_called_with(None, None, None) + +Calls to magic methods do not appear in :attr:`~Mock.method_calls`, but they +are recorded in :attr:`~Mock.mock_calls`. + +.. 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 `AttributeError`. + +The full list of supported magic methods is: + +* ``__hash__``, ``__sizeof__``, ``__repr__`` and ``__str__`` +* ``__dir__``, ``__format__`` and ``__subclasses__`` +* ``__floor__``, ``__trunc__`` and ``__ceil__`` +* Comparisons: ``__cmp__``, ``__lt__``, ``__gt__``, ``__le__``, ``__ge__``, + ``__eq__`` and ``__ne__`` +* Container methods: ``__getitem__``, ``__setitem__``, ``__delitem__``, + ``__contains__``, ``__len__``, ``__iter__``, ``__getslice__``, + ``__setslice__``, ``__reversed__`` and ``__missing__`` +* Context manager: ``__enter__`` and ``__exit__`` +* Unary numeric methods: ``__neg__``, ``__pos__`` and ``__invert__`` +* The numeric methods (including right hand and in-place variants): + ``__add__``, ``__sub__``, ``__mul__``, ``__div__``, + ``__floordiv__``, ``__mod__``, ``__divmod__``, ``__lshift__``, + ``__rshift__``, ``__and__``, ``__xor__``, ``__or__``, and ``__pow__`` +* Numeric conversion methods: ``__complex__``, ``__int__``, ``__float__``, + ``__index__`` and ``__coerce__`` +* Descriptor methods: ``__get__``, ``__set__`` and ``__delete__`` +* Pickling: ``__reduce__``, ``__reduce_ex__``, ``__getinitargs__``, + ``__getnewargs__``, ``__getstate__`` and ``__setstate__`` + + +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: + +* ``__getattr__``, ``__setattr__``, ``__init__`` and ``__new__`` +* ``__prepare__``, ``__instancecheck__``, ``__subclasscheck__``, ``__del__`` + + + +Magic Mock +---------- + +There are two `MagicMock` variants: `MagicMock` and `NonCallableMagicMock`. + + +.. class:: MagicMock(*args, **kw) + + ``MagicMock`` is a subclass of :class:`Mock` with default implementations + of most of the magic methods. You can use ``MagicMock`` without having to + configure the magic methods yourself. + + The constructor parameters have the same meaning as for :class:`Mock`. + + If you use the `spec` or `spec_set` arguments then *only* magic methods + that exist in the spec will be created. + + +.. class:: NonCallableMagicMock(*args, **kw) + + A non-callable version of `MagicMock`. + + The constructor parameters have the same meaning as for + :class:`MagicMock`, with the exception of `return_value` and + `side_effect` which have no meaning on a non-callable mock. + +The magic methods are setup with `MagicMock` objects, so you can configure them +and use them in the usual way: + + >>> mock = MagicMock() + >>> mock[3] = 'fish' + >>> mock.__setitem__.assert_called_with(3, 'fish') + >>> mock.__getitem__.return_value = 'result' + >>> mock[2] + 'result' + +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: + +* ``__lt__``: NotImplemented +* ``__gt__``: NotImplemented +* ``__le__``: NotImplemented +* ``__ge__``: NotImplemented +* ``__int__`` : 1 +* ``__contains__`` : False +* ``__len__`` : 1 +* ``__iter__`` : iter([]) +* ``__exit__`` : False +* ``__complex__`` : 1j +* ``__float__`` : 1.0 +* ``__bool__`` : True +* ``__index__`` : 1 +* ``__hash__`` : default hash for the mock +* ``__str__`` : default str for the mock +* ``__sizeof__``: default sizeof for the mock + +For example: + + >>> mock = MagicMock() + >>> int(mock) + 1 + >>> len(mock) + 0 + >>> list(mock) + [] + >>> object() in mock + False + +The two equality method, `__eq__` and `__ne__`, are special. +They do the default equality comparison on identity, using a side +effect, unless you change their return value to return something else: + + >>> MagicMock() == 3 + False + >>> MagicMock() != 3 + True + >>> mock = MagicMock() + >>> mock.__eq__.return_value = True + >>> mock == 3 + True + +The return value of `MagicMock.__iter__` can be any iterable object and isn't +required to be an iterator: + + >>> mock = MagicMock() + >>> mock.__iter__.return_value = ['a', 'b', 'c'] + >>> list(mock) + ['a', 'b', 'c'] + >>> list(mock) + ['a', 'b', 'c'] + +If the return value *is* an iterator, then iterating over it once will consume +it and subsequent iterations will result in an empty list: + + >>> mock.__iter__.return_value = iter(['a', 'b', 'c']) + >>> list(mock) + ['a', 'b', 'c'] + >>> list(mock) + [] + +``MagicMock`` 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 ``MagicMock`` are: + +* ``__subclasses__`` +* ``__dir__`` +* ``__format__`` +* ``__get__``, ``__set__`` and ``__delete__`` +* ``__reversed__`` and ``__missing__`` +* ``__reduce__``, ``__reduce_ex__``, ``__getinitargs__``, ``__getnewargs__``, + ``__getstate__`` and ``__setstate__`` +* ``__getformat__`` and ``__setformat__`` + + + +.. [#] 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. +.. [#] The function is basically hooked up to the class, but each ``Mock`` + instance is kept isolated from the others. |