The Tor Browser: comparison python/mock-1.0.0/docs/getting-started.txt

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+:44ba3d9f3268
+===========================
+Getting Started with Mock
+===========================
+.. _getting-started:
+.. index:: Getting Started
+.. testsetup::
+class SomeClass(object):
+static_method = None
+class_method = None
+attribute = None
+sys.modules['package'] = package = Mock(name='package')
+sys.modules['package.module'] = module = package.module
+sys.modules['module'] = package.module
+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:
+.. doctest::
+>>> 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:
+.. doctest::
+>>> from mock import MagicMock
+>>> 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.
+.. doctest::
+>>> 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.
+.. doctest::
+>>> 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 modifying the mock :attr:`~Mock.return_value`.
+.. doctest::
+>>> 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:
+.. doctest::
+>>> 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.
+.. doctest::
+>>> 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`:
+.. doctest::
+>>> 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:
+.. doctest::
+>>> mock = Mock()
+>>> mock.return_value = 3
+>>> mock()
+3
+Of course you can do the same for methods on the mock:
+.. doctest::
+>>> mock = Mock()
+>>> mock.method.return_value = 3
+>>> mock.method()
+3
+The return value can also be set in the constructor:
+.. doctest::
+>>> mock = Mock(return_value=3)
+>>> mock()
+3
+If you need an attribute setting on your mock, just do it:
+.. doctest::
+>>> 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:
+.. doctest::
+>>> 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.
+.. doctest::
+>>> 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:
+.. doctest::
+>>> 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:
+.. doctest::
+>>> 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.
+.. doctest::
+>>> 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`:
+.. doctest::
+>>> 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`:
+.. doctest::
+>>> 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:
+.. doctest::
+>>> @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:
+.. doctest::
+>>> 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:
+.. doctest::
+>>> 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:
+.. doctest::
+>>> 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:
+.. doctest::
+>>> 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:
+.. doctest::
+>>> 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.

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python/mock-1.0.0/docs/getting-started.txt