# `unittest.mock` --- mock对象库

3.3 新版功能.

源代码： Lib/unittest/mock.py

`unittest.mock` 是一个用于测试的Python库。它允许使用mock对象替换受测试系统的部分，并对它们如何已经被使用进行断言。

`unittest.mock` 提供的 `Mock` 类，能在整个测试套件中模拟大量的方法。创建后，就可以断言调用了哪些方法/属性及其参数。还可以以常规方式指定返回值并设置所需的属性。

此外，mock 提供了用于修补测试范围内模块和类级别属性的 `patch()` 装饰器，和用于创建独特对象的 `sentinel` 。 阅读 quick guide 中的案例了解如何使用 `Mock` ，`MagicMock` 和 `patch()` 。

mock 被设计为配合 `unittest` 使用且它是基于 'action -> assertion' 模式而非许多模拟框架所使用的 'record -> replay' 模式。

在 Python 的早期版本要单独使用 `unittest.mock` ，在 PyPI 获取 mock 。

## 快速上手

当您访问对象时， `Mock` 和 `MagicMock` 将创建所有属性和方法，并保存他们在使用时的细节。你可以通过配置，指定返回值或者限制可访问属性，然后断言他们如何被调用：

    >>> from unittest.mock import MagicMock
    >>> thing = ProductionClass()
    >>> thing.method = MagicMock(return_value=3)
    >>> thing.method(3, 4, 5, key='value')
    3
    >>> thing.method.assert_called_with(3, 4, 5, key='value')

通过 `side_effect` 设置副作用(side effects) ，可以是一个 mock 被调用是抛出的异常：

    >>> mock = Mock(side_effect=KeyError('foo'))
    >>> mock()
    Traceback (most recent call last):
     ...
    KeyError: 'foo'

    >>> values = {'a': 1, 'b': 2, 'c': 3}
    >>> def side_effect(arg):
    ...     return values[arg]
    ...
    >>> mock.side_effect = side_effect
    >>> mock('a'), mock('b'), mock('c')
    (1, 2, 3)
    >>> mock.side_effect = [5, 4, 3, 2, 1]
    >>> mock(), mock(), mock()
    (5, 4, 3)

Mock 还可以通过其他方法配置和控制其行为。例如 mock 可以通过设置 spec 参数来从一个对象中获取其规格(specification)。如果访问 mock 的属性或方法不在 spec 中，会报 `AttributeError` 错误。

使用 `patch()` 装饰去/上下文管理器，可以更方便地测试一个模块下的类或对象。你指定的对象会在测试过程中替换成 mock （或者其他对象），测试结束后恢复。

    >>> from unittest.mock import patch
    >>> @patch('module.ClassName2')
    ... @patch('module.ClassName1')
    ... def test(MockClass1, MockClass2):
    ...     module.ClassName1()
    ...     module.ClassName2()
    ...     assert MockClass1 is module.ClassName1
    ...     assert MockClass2 is module.ClassName2
    ...     assert MockClass1.called
    ...     assert MockClass2.called
    ...
    >>> test()

注解

当你嵌套 patch 装饰器时，mock 将以执行顺序传递给装饰器函数（Python 装饰器正常顺序）。由于从下至上，因此在上面的示例中，首先 mock 传入的 `module.ClassName1` 。

在查找对象的名称空间中修补对象使用 `patch()` 。使用起来很简单，阅读 在哪里打补丁 来快速上手。

`patch()` 也可以 with 语句中使用上下文管理。

    >>> with patch.object(ProductionClass, 'method', return_value=None) as mock_method:
    ...     thing = ProductionClass()
    ...     thing.method(1, 2, 3)
    ...
    >>> mock_method.assert_called_once_with(1, 2, 3)

还有一个 `patch.dict()` 用于在一定范围内设置字典中的值，并在测试结束时将字典恢复为其原始状态：

    >>> foo = {'key': 'value'}
    >>> original = foo.copy()
    >>> with patch.dict(foo, {'newkey': 'newvalue'}, clear=True):
    ...     assert foo == {'newkey': 'newvalue'}
    ...
    >>> assert foo == original

Mock支持 Python 魔术方法 。使用模式方法最简单的方式是使用 `MagicMock` class. 。它可以做如下事情：

    >>> mock = MagicMock()
    >>> mock.__str__.return_value = 'foobarbaz'
    >>> str(mock)
    'foobarbaz'
    >>> mock.__str__.assert_called_with()

Mock 能指定函数（或其他 Mock 实例）为魔术方法，它们将被适当地调用。 `MagicMock` 是预先创建了所有魔术方法（所有有用的方法） 的 Mock 。

下面是一个使用了普通 Mock 类的魔术方法的例子

    >>> mock = Mock()
    >>> mock.__str__ = Mock(return_value='wheeeeee')
    >>> str(mock)
    'wheeeeee'

使用 auto-speccing 可以保证测试中的模拟对象与要替换的对象具有相同的api 。在 patch 中可以通过 autospec 参数实现自动推断，或者使用 `create_autospec()` 函数。自动推断会创建一个与要替换对象相同的属相和方法的模拟对象，并且任何函数和方法（包括构造函数）都具有与真实对象相同的调用签名。

这么做是为了因确保不当地使用 mock 导致与生产代码相同的失败：

    >>> from unittest.mock import create_autospec
    >>> def function(a, b, c):
    ...     pass
    ...
    >>> mock_function = create_autospec(function, return_value='fishy')
    >>> mock_function(1, 2, 3)
    'fishy'
    >>> mock_function.assert_called_once_with(1, 2, 3)
    >>> mock_function('wrong arguments')
    Traceback (most recent call last):
     ...
    TypeError: <lambda>() takes exactly 3 arguments (1 given)

在类中使用 `create_autospec()` 时，会复制 `__init__` 方法的签名，另外在可调用对象上使用时，会复制 `__call__` 方法的签名。

## Mock 类

`Mock` 是一个可以灵活的替换存根 (stubs) 的对象，可以测试所有代码。 Mock 是可调用的，在访问其属性时创建一个新的 mock 1 。访问相同的属性只会返回相同的 mock 。 Mock 会保存调用记录，可以通过断言获悉代码的调用。

`MagicMock` 是 `Mock` 的子类，它有所有预创建且可使用的魔术方法。在需要模拟不可调用对象时，可以使用 `NonCallableMock` 和 `NonCallableMagicMock`

`patch()` 装饰器便于 `Mock` 对象临时替换特定模块中的类。 `patch()` 默认创建 `MagicMock` 。可以使用 `patch()` 方法的 new_callable 参数指定 `Mock` 的替代类。

class `unittest.mock.``Mock`(spec=None, side_effect=None, return_value=DEFAULT, wraps=None, name=None, spec_set=None, unsafe=False, **kwargs)

  创建一个新的 `Mock` 对象。通过可选参数指定 `Mock` 对象的行为：

  - spec: 可以是要给字符串列表，也可以是充当模拟对象规范的现有对象（类或实例）。如果传入一个对象，则通过在该对象上调用 dir 来生成字符串列表（不支持的魔法属性和方法除外）。访问不在此列表中的任何属性都将触发 `AttributeError` 。

    如果 spec 是一个对象（而不是字符串列表），则 `__class__` 返回 spec 对象的类。 这允许模拟程序通过 `isinstance()` 测试。

  - spec_set ：spec 的更严格的变体。如果使用了该属性，尝试模拟 set 或 get 的属性不在 spec_set 所包含的对象中时，会抛出 `AttributeError` 。

  - side_effect ：每当调用 Mock 时都会调用的函数。 参见 `side_effect` 属性。 对于引发异常或动态更改返回值很有用。 该函数使用与 mock 函数相同的参数调用，并且除非返回 `DEFAULT` ，否则该函数的返回值将用作返回值。

    另外， side_effect 可以是异常类或实例。 此时，调用模拟程序时将引发异常。

    如果 side_effect 是可迭代对象，则每次调用 mock 都将返回可迭代对象的下一个值。

    设置 side_effect 为 `None` 即可清空。

  - return_value ：调用 mock 的返回值。 默认情况下，是一个新的Mock（在首次访问时创建）。 参见 `return_value` 属性 。

  - unsafe ：默认情况下，如果任何以 assert 或 assret 开头的属性都将引发 `AttributeError` 。 当 `unsafe=True` 时可以访问。

    3.5 新版功能.

  - wraps ：要包装的 mock 对象。 如果 wraps 不是 `None` ，那么调用 Mock 会将调用传递给 wraps 的对象（返回实际结果）。 对模拟的属性访问将返回一个 Mock 对象，该对象包装了 wraps 对象的相应属性（因此，尝试访问不存在的属性将引发 `AttributeError` ）。

    如果明确指定 return_value ，调用是，不会返回包装对象，而是返回 return_value 。

  - name ：mock 的名称。 在调试时很有用。 名称会传递到子 mock 。

  还可以使用任意关键字参数来调用 mock 。 创建模拟后，将使用这些属性来设置 mock 的属性。 有关详细信息，请参见 `configure_mock()` 方法。

  `assert_called`()

    断言至少被调用过一次。

        >>> mock = Mock()
        >>> mock.method()
        <Mock name='mock.method()' id='...'>
        >>> mock.method.assert_called()

    3.6 新版功能.

  `assert_called_once`()

    断言仅被调用一次。

        >>> mock = Mock()
        >>> mock.method()
        <Mock name='mock.method()' id='...'>
        >>> mock.method.assert_called_once()
        >>> mock.method()
        <Mock name='mock.method()' id='...'>
        >>> mock.method.assert_called_once()
        Traceback (most recent call last):
        ...
        AssertionError: Expected 'method' to have been called once. Called 2 times.

    3.6 新版功能.

  `assert_called_with`(*args, **kwargs)

    此方法是断言上次调用已以特定方式进行的一种便捷方法：

        >>> mock = Mock()
        >>> mock.method(1, 2, 3, test='wow')
        <Mock name='mock.method()' id='...'>
        >>> mock.method.assert_called_with(1, 2, 3, test='wow')

  `assert_called_once_with`(*args, **kwargs)

    断言 mock 仅被调用一次，并且向该调用传入了指定的参数。

        >>> mock = Mock(return_value=None)
        >>> mock('foo', bar='baz')
        >>> mock.assert_called_once_with('foo', bar='baz')
        >>> mock('other', bar='values')
        >>> mock.assert_called_once_with('other', bar='values')
        Traceback (most recent call last):
          ...
        AssertionError: Expected 'mock' to be called once. Called 2 times.

  `assert_any_call`(*args, **kwargs)

    断言使用指定的参数调用。

    如果 mock 曾经 被调用过则断言通过，不同于 `assert_called_with()` 和 `assert_called_once_with()` 那样只有在调用是最近的一次时才会通过，而对于 `assert_called_once_with()` 则它还必须是唯一的一次调用。

        >>> mock = Mock(return_value=None)
        >>> mock(1, 2, arg='thing')
        >>> mock('some', 'thing', 'else')
        >>> mock.assert_any_call(1, 2, arg='thing')

  `assert_has_calls`(calls, any_order=False)

    断言 mock 已附带指定的参数被调用。 将针对这些调用检查 `mock_calls` 列表。

    如果 any_order 为假值则调用必须是顺序进行的。 在指定的调用之前或之后还可以有额外的调用。

    如果 any_order 为真值则调用可以是任意顺序的，但它们都必须在 `mock_calls` 中出现。

        >>> mock = Mock(return_value=None)
        >>> mock(1)
        >>> mock(2)
        >>> mock(3)
        >>> mock(4)
        >>> calls = [call(2), call(3)]
        >>> mock.assert_has_calls(calls)
        >>> calls = [call(4), call(2), call(3)]
        >>> mock.assert_has_calls(calls, any_order=True)

  `assert_not_called`()

    断言 mock 从未被调用过。

        >>> m = Mock()
        >>> m.hello.assert_not_called()
        >>> obj = m.hello()
        >>> m.hello.assert_not_called()
        Traceback (most recent call last):
          ...
        AssertionError: Expected 'hello' to not have been called. Called 1 times.

    3.5 新版功能.

  `reset_mock`(*, return_value=False, side_effect=False)

    reset_mock 方法将在 mock 对象上重围所有的调用属性:

        >>> mock = Mock(return_value=None)
        >>> mock('hello')
        >>> mock.called
        True
        >>> mock.reset_mock()
        >>> mock.called
        False

    在 3.6 版更改: 向 reset_mock 函数添加了两个仅限关键字参数。

    这在你想要创建一系列重用相同对象的断言时会很有用处。 请注意 `reset_mock()` 不会 清除返回值、`side_effect` 或任何你使用普通赋值所默认设置的子属性。 如果你想要重置 return_value 或 `side_effect`，则要为相应的形参传入 `True`。 子 mock 和返回值 mock (如果有的话) 也会被重置。

    注解

    return_value 和 `side_effect` 均为仅限关键字参数。

  `mock_add_spec`(spec, spec_set=False)

    为 mock 添加规格说明。 spec 可以是一个对象或字符串列表。 只有 spec 上的属性可以作为来自 mock 的属性被获取。

    如果 spec_set 为真值则只有 spec 上的属性可以被设置。

  `attach_mock`(mock, attribute)

    附加一个 mock 作为这一个的属性，替换它的名称和上级。 对附加 mock 的调用将记录在这一个的 `method_calls` 和 `mock_calls` 属性中。

  `configure_mock`(**kwargs)

    通过关键字参数在 mock 上设置属性。

    属性加返回值和附带影响可以使用标准点号标记在子 mock 上设置并在方法调用中解包一个字典:

        >>> mock = Mock()
        >>> attrs = {'method.return_value': 3, 'other.side_effect': KeyError}
        >>> mock.configure_mock(**attrs)
        >>> mock.method()
        3
        >>> mock.other()
        Traceback (most recent call last):
          ...
        KeyError

    同样的操作可在对 mock 的构造器调用中达成:

        >>> attrs = {'method.return_value': 3, 'other.side_effect': KeyError}
        >>> mock = Mock(some_attribute='eggs', **attrs)
        >>> mock.some_attribute
        'eggs'
        >>> mock.method()
        3
        >>> mock.other()
        Traceback (most recent call last):
          ...
        KeyError

    `configure_mock()` 的存在是使得 mock 被创建之后的配置更为容易。

  `__dir__`()

    `Mock` 对象会将 `dir(some_mock)` 的结果限制为有用结果。 对于带有 spec 的 mock 这还包括 mock 的所有被允许的属性。

    请查看 `FILTER_DIR` 了解此过滤做了什么，以及如何停用它。

  `_get_child_mock`(**kw)

    创建针对属性和返回值的子 mock。 默认情况下子 mock 将为与其上级相同的类型。 Mock 的子类可能需要重载它来定制子 mock 的创建方式。

    对于非可调用的 mock 将会使用可调用的变化形式（而非不是任意的自定义子类）。

  `called`

    一个表示 mock 对象是否已被调用的布尔值:

        >>> mock = Mock(return_value=None)
        >>> mock.called
        False
        >>> mock()
        >>> mock.called
        True

  `call_count`

    一个告诉你 mock object 对象已被调用多少次的整数值:

        >>> mock = Mock(return_value=None)
        >>> mock.call_count
        0
        >>> mock()
        >>> mock()
        >>> mock.call_count
        2

  `return_value`

    设置这个来配置通过调用该 mock 所返回的值:

        >>> mock = Mock()
        >>> mock.return_value = 'fish'
        >>> mock()
        'fish'

    默认的返回值是一个 mock 对象并且你可以通过正常方式来配置它:

        >>> mock = Mock()
        >>> mock.return_value.attribute = sentinel.Attribute
        >>> mock.return_value()
        <Mock name='mock()()' id='...'>
        >>> mock.return_value.assert_called_with()

    `return_value` 也可以在构造器中设置:

        >>> mock = Mock(return_value=3)
        >>> mock.return_value
        3
        >>> mock()
        3

  `side_effect`

    这可以是当该This can either be a function to be called when the mock 被调用时将被调用的一个函数，可调用对象或者要被引发的异常（类或实例）。

    如果你传入一个函数则它将附带与该 mock 相同的参数被调用并且除了该函数返回 `DEFAULT` 单例的情况以外对该 mock 的调用都将随后返回该函数所返回的任何东西。 如果该函数返回 `DEFAULT` 则该 mock 将返回其正常值 (来自 `return_value`)。

    如果你传入一个可迭代对象，它会被用来获取一个在每次调用时必须产生一个值的迭代器。 这个值可以是一个要被引发的异常实例，或是一个要从该调用返回给 mock 的值 (`DEFAULT` 处理与函数的情况一致)。

    一个引发异常（来测试 API 的异常处理）的 mock 的示例:

        >>> mock = Mock()
        >>> mock.side_effect = Exception('Boom!')
        >>> mock()
        Traceback (most recent call last):
          ...
        Exception: Boom!

    使用 `side_effect` 来返回包含多个值的序列:

        >>> mock = Mock()
        >>> mock.side_effect = [3, 2, 1]
        >>> mock(), mock(), mock()
        (3, 2, 1)

    使用一个可调用对象:

        >>> mock = Mock(return_value=3)
        >>> def side_effect(*args, **kwargs):
        ...     return DEFAULT
        ...
        >>> mock.side_effect = side_effect
        >>> mock()
        3

    `side_effect` 可以在构造器中设置。 下面是在 mock 被调用时增加一个该属性值并返回它的例子:

        >>> side_effect = lambda value: value + 1
        >>> mock = Mock(side_effect=side_effect)
        >>> mock(3)
        4
        >>> mock(-8)
        -7

    将 `side_effect` 设为 `None` 可以清除它:

        >>> m = Mock(side_effect=KeyError, return_value=3)
        >>> m()
        Traceback (most recent call last):
         ...
        KeyError
        >>> m.side_effect = None
        >>> m()
        3

  `call_args`

    这可以是 `None` (如果 mock 没有被调用)，或是 mock 最近一次被调用时附带的参数。 这将采用元组的形式：第一个成员也可以通过 `args` 特征属性来访问，它是 mock 被调用时所附带的任何位置参数 (或为空元组)，而第二个成员也可以通过 `kwargs` 特征属性来访问，它则是任何关键字参数 (或为空字典)。

        >>> mock = Mock(return_value=None)
        >>> print(mock.call_args)
        None
        >>> mock()
        >>> mock.call_args
        call()
        >>> mock.call_args == ()
        True
        >>> mock(3, 4)
        >>> mock.call_args
        call(3, 4)
        >>> mock.call_args == ((3, 4),)
        True
        >>> mock.call_args.args
        (3, 4)
        >>> mock.call_args.kwargs
        {}
        >>> mock(3, 4, 5, key='fish', next='w00t!')
        >>> mock.call_args
        call(3, 4, 5, key='fish', next='w00t!')
        >>> mock.call_args.args
        (3, 4, 5)
        >>> mock.call_args.kwargs
        {'key': 'fish', 'next': 'w00t!'}

    `call_args`，以及列表 `call_args_list`, `method_calls` 和 `mock_calls` 的成员都是 `call` 对象。 这些对象属性元组，因此它们可被解包以获得单独的参数并创建更复杂的断言。 参见 作为元组的 call。

    在 3.8 版更改: 增加了 `args` 和 `kwargs` 特征属性。properties.

  `call_args_list`

    这是一个已排序的对 mock 对象的所有调用的列表（因此该列表的长度就是它已被调用的次数）。 在执行任何调用之前它将是一个空列表。 `call` 对象可以被用来方便地构造调用列表以与 `call_args_list` 相比较。

        >>> mock = Mock(return_value=None)
        >>> mock()
        >>> mock(3, 4)
        >>> mock(key='fish', next='w00t!')
        >>> mock.call_args_list
        [call(), call(3, 4), call(key='fish', next='w00t!')]
        >>> expected = [(), ((3, 4),), ({'key': 'fish', 'next': 'w00t!'},)]
        >>> mock.call_args_list == expected
        True

    `call_args_list` 的成员均为 `call` 对象。 它们可作为元组被解包以获得单个参数。 参见 作为元组的 call。

  `method_calls`

    除了会追踪对其自身的调用，mock 还会追踪对方法和属性，以及 它们的 方法和属性的访问:

        >>> mock = Mock()
        >>> mock.method()
        <Mock name='mock.method()' id='...'>
        >>> mock.property.method.attribute()
        <Mock name='mock.property.method.attribute()' id='...'>
        >>> mock.method_calls
        [call.method(), call.property.method.attribute()]

    `method_calls` 的成员均为 `call` 对象。 它们可以作为元组被解包以获得单个参数。 参见 作为元组的 call.

  `mock_calls`

    `mock_calls` 会记录 所有 对 mock 对象、它的方法、魔术方法的调用 以及 返回值的 mock。

        >>> mock = MagicMock()
        >>> result = mock(1, 2, 3)
        >>> mock.first(a=3)
        <MagicMock name='mock.first()' id='...'>
        >>> mock.second()
        <MagicMock name='mock.second()' id='...'>
        >>> int(mock)
        1
        >>> result(1)
        <MagicMock name='mock()()' id='...'>
        >>> expected = [call(1, 2, 3), call.first(a=3), call.second(),
        ... call.__int__(), call()(1)]
        >>> mock.mock_calls == expected
        True

    `mock_calls` 的成员均为 `call` 对象。 它们可以作为元组被解包以获得单个参数。 参见 作为元组的 call。

    注解

    `mock_calls` 的记录方式意味着在进行嵌套调用时，之前调用的形参不会被记录因而这样的比较将总是相等:

        >>> mock = MagicMock()
        >>> mock.top(a=3).bottom()
        <MagicMock name='mock.top().bottom()' id='...'>
        >>> mock.mock_calls
        [call.top(a=3), call.top().bottom()]
        >>> mock.mock_calls[-1] == call.top(a=-1).bottom()
        True

  `__class__`

    通常一个对象的 `__class__` 属性将返回其类型。 对于具有 `spec` 的 mock 对象来说，`__class__` 将改为返回 spec 类。 这将允许 mock 对象为它们所替换 / 屏蔽的对象跳过 `isinstance()` 测试:

        >>> mock = Mock(spec=3)
        >>> isinstance(mock, int)
        True

    `__class__` 是可以被赋值的，这将允许 mock 跳过 `isinstance()` 检测而不强制要求你使用 spec:

        >>> mock = Mock()
        >>> mock.__class__ = dict
        >>> isinstance(mock, dict)
        True

class `unittest.mock.``NonCallableMock`(spec=None, wraps=None, name=None, spec_set=None, **kwargs)

  不可调用的 `Mock` 版本。 其构造器的形参具有与 `Mock` 相同的含义，区别在于 return_value 和 side_effect 在不可调用的 mock 上没有意义。

使用类或实例作为 `spec` 或 `spec_set` 的 mock 对象能够跳过 `isinstance()` 测试:

    >>> mock = Mock(spec=SomeClass)
    >>> isinstance(mock, SomeClass)
    True
    >>> mock = Mock(spec_set=SomeClass())
    >>> isinstance(mock, SomeClass)
    True

`Mock` 类具有对模拟魔术方法的支持。 请参阅 魔术方法 了解完整细节。

mock 操作类和 `patch()` 装饰器都接受任意关键字参数用于配置。 对于 `patch()` 装饰器来说关键字参数会被传给所创建 mock 的构造器。 这些关键字被用于配置 mock 的属性:

    >>> m = MagicMock(attribute=3, other='fish')
    >>> m.attribute
    3
    >>> m.other
    'fish'

子 mock 的返回值和附带效果也可使用带点号的标记通过相同的方式来设置。 由于你无法直接在调用中使用带点号的名称因此你需要创建一个字典并使用 `**` 来解包它:

    >>> attrs = {'method.return_value': 3, 'other.side_effect': KeyError}
    >>> mock = Mock(some_attribute='eggs', **attrs)
    >>> mock.some_attribute
    'eggs'
    >>> mock.method()
    3
    >>> mock.other()
    Traceback (most recent call last):
      ...
    KeyError

使用 spec (或 spec_set) 创建的可调用 mock 将在匹配调用与 mock 时内省规格说明对象的签名。 因此，它可以匹配实际调用的参数而不必关心它们是按位置还是按名称传入的:

    >>> def f(a, b, c): pass
    ...
    >>> mock = Mock(spec=f)
    >>> mock(1, 2, c=3)
    <Mock name='mock()' id='140161580456576'>
    >>> mock.assert_called_with(1, 2, 3)
    >>> mock.assert_called_with(a=1, b=2, c=3)

这适用于 `assert_called_with()`, `assert_called_once_with()`, `assert_has_calls()` 和 `assert_any_call()`。 当执行 Autospeccing 时，它还将应用于 mock 对象的方法调用。

> 在 3.4 版更改: 添加了在附带规格说明和自动规格说明的 mock 对象上的签名内省

class `unittest.mock.``PropertyMock`(*args, **kwargs)

  旨在作为类的特征属性或其他描述器使用的 mock。 `PropertyMock` 提供了 `__get__()` 和 `__set__()` 方法以便你可以在它被提取时指定一个返回值。

  当从一个对象提取 `PropertyMock` 实例时将不附带任何参数地调用该 mock。 如果设置它则调用该 mock 时将附带被设置的值。

      >>> class Foo:
      ...     @property
      ...     def foo(self):
      ...         return 'something'
      ...     @foo.setter
      ...     def foo(self, value):
      ...         pass
      ...
      >>> with patch('__main__.Foo.foo', new_callable=PropertyMock) as mock_foo:
      ...     mock_foo.return_value = 'mockity-mock'
      ...     this_foo = Foo()
      ...     print(this_foo.foo)
      ...     this_foo.foo = 6
      ...
      mockity-mock
      >>> mock_foo.mock_calls
      [call(), call(6)]

由于 mock 属性的存储方式你无法直接将 `PropertyMock` 附加到一个 mock 对象。 但是你可以将它附加到 mock 类型对象:

    >>> m = MagicMock()
    >>> p = PropertyMock(return_value=3)
    >>> type(m).foo = p
    >>> m.foo
    3
    >>> p.assert_called_once_with()

class `unittest.mock.``AsyncMock`(spec=None, side_effect=None, return_value=DEFAULT, wraps=None, name=None, spec_set=None, unsafe=False, **kwargs)

  `MagicMock` 的异步版本。 `AsyncMock` 对象的行为方式将使该对象被识别为异步函数，其调用的结果将为可等待对象。

      >>> mock = AsyncMock()
      >>> asyncio.iscoroutinefunction(mock)
      True
      >>> inspect.isawaitable(mock())
      True

  调用 `mock()` 的结果是一个异步函数，它在被等待之后将具有 `side_effect` 或 `return_value` 的结果:

  - 如果 `side_effect` 是一个函数，则异步函数将返回该函数的结果,

  - 如果 `side_effect` 是一个异常，则异步函数将引发该异常,

  - 如果 `side_effect` 是一个可迭代对象，则异步函数将返回该可迭代对象的下一个值，但是，如果结果序列被耗尽，则会立即引发 `StopAsyncIteration`,

  - 如果 `side_effect` 未被定义，则异步函数将返回is not defined, the async function will return the value defined by `return_value` 所定义的值，因而，在默认情况下，异步函数会返回一个新的 `AsyncMock` 对象。

  将 `Mock` 或 `MagicMock` 的 spec 设为异步函数将导致在调用后返回一个协程对象。

      >>> async def async_func(): pass
      ...
      >>> mock = MagicMock(async_func)
      >>> mock
      <MagicMock spec='function' id='...'>
      >>> mock()
      <coroutine object AsyncMockMixin._mock_call at ...>

  将 `Mock`, `MagicMock` 或 `AsyncMock` 的 spec 设为带有异步和同步函数的类将自动删除其中的同步函数并将它们设为 `MagicMock` (如果上级 mock 是 `AsyncMock` 或 `MagicMock`) 或者 `Mock` (如果上级 mock 是 `Mock`)。 所有异步函数都将为 `AsyncMock`。

      >>> class ExampleClass:
      ...     def sync_foo():
      ...         pass
      ...     async def async_foo():
      ...         pass
      ...
      >>> a_mock = AsyncMock(ExampleClass)
      >>> a_mock.sync_foo
      <MagicMock name='mock.sync_foo' id='...'>
      >>> a_mock.async_foo
      <AsyncMock name='mock.async_foo' id='...'>
      >>> mock = Mock(ExampleClass)
      >>> mock.sync_foo
      <Mock name='mock.sync_foo' id='...'>
      >>> mock.async_foo
      <AsyncMock name='mock.async_foo' id='...'>

  3.8 新版功能.

  `assert_awaited`()

    断言 mock 已被等待至少一次。 请注意这是从被调用的对象中分离出来的，必须要使用 `await` 关键字:

        >>> mock = AsyncMock()
        >>> async def main(coroutine_mock):
        ...     await coroutine_mock
        ...
        >>> coroutine_mock = mock()
        >>> mock.called
        True
        >>> mock.assert_awaited()
        Traceback (most recent call last):
        ...
        AssertionError: Expected mock to have been awaited.
        >>> asyncio.run(main(coroutine_mock))
        >>> mock.assert_awaited()

  `assert_awaited_once`()

    断言 mock 已被等待恰好一次。

        >>> mock = AsyncMock()
        >>> async def main():
        ...     await mock()
        ...
        >>> asyncio.run(main())
        >>> mock.assert_awaited_once()
        >>> asyncio.run(main())
        >>> mock.method.assert_awaited_once()
        Traceback (most recent call last):
        ...
        AssertionError: Expected mock to have been awaited once. Awaited 2 times.

  `assert_awaited_with`(*args, **kwargs)

    断言上一次等待传入了指定的参数。

        >>> mock = AsyncMock()
        >>> async def main(*args, **kwargs):
        ...     await mock(*args, **kwargs)
        ...
        >>> asyncio.run(main('foo', bar='bar'))
        >>> mock.assert_awaited_with('foo', bar='bar')
        >>> mock.assert_awaited_with('other')
        Traceback (most recent call last):
        ...
        AssertionError: expected call not found.
        Expected: mock('other')
        Actual: mock('foo', bar='bar')

  `assert_awaited_once_with`(*args, **kwargs)

    断言 mock 被等待恰好一次并且附带了指定的参数。

        >>> mock = AsyncMock()
        >>> async def main(*args, **kwargs):
        ...     await mock(*args, **kwargs)
        ...
        >>> asyncio.run(main('foo', bar='bar'))
        >>> mock.assert_awaited_once_with('foo', bar='bar')
        >>> asyncio.run(main('foo', bar='bar'))
        >>> mock.assert_awaited_once_with('foo', bar='bar')
        Traceback (most recent call last):
        ...
        AssertionError: Expected mock to have been awaited once. Awaited 2 times.

  `assert_any_await`(*args, **kwargs)

    断言 mock 已被等待并附带了指定的参数。

        >>> mock = AsyncMock()
        >>> async def main(*args, **kwargs):
        ...     await mock(*args, **kwargs)
        ...
        >>> asyncio.run(main('foo', bar='bar'))
        >>> asyncio.run(main('hello'))
        >>> mock.assert_any_await('foo', bar='bar')
        >>> mock.assert_any_await('other')
        Traceback (most recent call last):
        ...
        AssertionError: mock('other') await not found

  `assert_has_awaits`(calls, any_order=False)

    断言 mock 已附带了指定的调用被等待。 将针对这些等待检查 `await_args_list` 列表。

    如果 any_order 为假值则等待必须是顺序进行的。 在指定的等待之前或之后还可以有额外的调用。

    如果 any_order 为真值则等待可以是任意顺序的，但它们都必须在 `await_args_list` 中出现。

        >>> mock = AsyncMock()
        >>> async def main(*args, **kwargs):
        ...     await mock(*args, **kwargs)
        ...
        >>> calls = [call("foo"), call("bar")]
        >>> mock.assert_has_awaits(calls)
        Traceback (most recent call last):
        ...
        AssertionError: Awaits not found.
        Expected: [call('foo'), call('bar')]
        Actual: []
        >>> asyncio.run(main('foo'))
        >>> asyncio.run(main('bar'))
        >>> mock.assert_has_awaits(calls)

  `assert_not_awaited`()

    断言 mock 从未被等待过。

        >>> mock = AsyncMock()
        >>> mock.assert_not_awaited()

  `reset_mock`(*args, **kwargs)

    参见 `Mock.reset_mock()`。 还会将 `await_count` 设为 0，将 `await_args` 设为 None，并清空 `await_args_list`。

  `await_count`

    一个追踪 mock 对象已被等待多少次的整数值。

        >>> mock = AsyncMock()
        >>> async def main():
        ...     await mock()
        ...
        >>> asyncio.run(main())
        >>> mock.await_count
        1
        >>> asyncio.run(main())
        >>> mock.await_count
        2

  `await_args`

    这可能为 `None` (如果 mock 从未被等待)，或为该 mock 上一次被等待所附带的参数。 其功能与 `Mock.call_args` 相同。

        >>> mock = AsyncMock()
        >>> async def main(*args):
        ...     await mock(*args)
        ...
        >>> mock.await_args
        >>> asyncio.run(main('foo'))
        >>> mock.await_args
        call('foo')
        >>> asyncio.run(main('bar'))
        >>> mock.await_args
        call('bar')

  `await_args_list`

    这是由对 mock 对象按顺序执行的所有等待组成的列表（因此该列表的长度即它被等待的次数）。 在有任何等待被执行之前它将为一个空列表。Before any awaits have been made it is an empty list.

        >>> mock = AsyncMock()
        >>> async def main(*args):
        ...     await mock(*args)
        ...
        >>> mock.await_args_list
        []
        >>> asyncio.run(main('foo'))
        >>> mock.await_args_list
        [call('foo')]
        >>> asyncio.run(main('bar'))
        >>> mock.await_args_list
        [call('foo'), call('bar')]

### 调用

Mock 对象是可调用对象。 调用将把值集合作为 `return_value` 属性返回。 默认的返回值是一个新的 Mock 对象；它会在对返回值的首次访问（不论是显式访问还是通过调用 Mock）时被创建 —— 但它会被保存并且每次都返回相同的对象。

对该对象的调用将被记录在 `call_args` 和 `call_args_list` 等属性中。

如果设置了 `side_effect` 则它将在调用被记录之后被调用，因此如果 `side_effect` 引发了异常该调用仍然会被记录。

让一个 mock 在被调用时引发异常的最简单方式是将 `side_effect` 设为一个异常类或实例:

    >>> m = MagicMock(side_effect=IndexError)
    >>> m(1, 2, 3)
    Traceback (most recent call last):
      ...
    IndexError
    >>> m.mock_calls
    [call(1, 2, 3)]
    >>> m.side_effect = KeyError('Bang!')
    >>> m('two', 'three', 'four')
    Traceback (most recent call last):
      ...
    KeyError: 'Bang!'
    >>> m.mock_calls
    [call(1, 2, 3), call('two', 'three', 'four')]

如果 `side_effect` 为函数则该函数所返回的对象就是调用该 mock 所返回的对象。 `side_effect` 函数在被调用时将附带与该 mock 相同的参数。 这允许你根据输入动态地改变返回值:

    >>> def side_effect(value):
    ...     return value + 1
    ...
    >>> m = MagicMock(side_effect=side_effect)
    >>> m(1)
    2
    >>> m(2)
    3
    >>> m.mock_calls
    [call(1), call(2)]

如果你想让该 mock 仍然返回默认的返回值（一个新的 mock对象），或是任何设定的返回值，那么有两种方式可以做到这一点。 从 `side_effect` 内部返回 `mock.return_value`，或者返回 `DEFAULT`:

    >>> m = MagicMock()
    >>> def side_effect(*args, **kwargs):
    ...     return m.return_value
    ...
    >>> m.side_effect = side_effect
    >>> m.return_value = 3
    >>> m()
    3
    >>> def side_effect(*args, **kwargs):
    ...     return DEFAULT
    ...
    >>> m.side_effect = side_effect
    >>> m()
    3

要移除一个 `side_effect`，并返回到默认的行为，请将 `side_effect` 设为 `None`:

    >>> m = MagicMock(return_value=6)
    >>> def side_effect(*args, **kwargs):
    ...     return 3
    ...
    >>> m.side_effect = side_effect
    >>> m()
    3
    >>> m.side_effect = None
    >>> m()
    6

`side_effect` 也可以是任意可迭代对象。 对该 mock 的重复调用将返回来自该可迭代对象的值（直到该可迭代对象被耗尽并导致 `StopIteration` 被引发）:

    >>> m = MagicMock(side_effect=[1, 2, 3])
    >>> m()
    1
    >>> m()
    2
    >>> m()
    3
    >>> m()
    Traceback (most recent call last):
      ...
    StopIteration

如果该可迭代对象有任何成员属于异常则它们将被引发而不是被返回:

    >>> iterable = (33, ValueError, 66)
    >>> m = MagicMock(side_effect=iterable)
    >>> m()
    33
    >>> m()
    Traceback (most recent call last):
     ...
    ValueError
    >>> m()
    66

### 删除属性

Mock 对象会根据需要创建属性。 这允许它们可以假装成任意类型的对象。

你可能想要一个 mock 对象在调用 `hasattr()` 时返回 `False`，或者在获取某个属性时引发 `AttributeError`。 你可以通过提供一个对象作为 mock 的 `spec` 属性来做到这点，但这并不总是很方便。

你可以通过删除属性来“屏蔽”它们。 属性一旦被删除，访问它将引发 `AttributeError`。

    >>> mock = MagicMock()
    >>> hasattr(mock, 'm')
    True
    >>> del mock.m
    >>> hasattr(mock, 'm')
    False
    >>> del mock.f
    >>> mock.f
    Traceback (most recent call last):
        ...
    AttributeError: f

### Mock 的名称与 name 属性

由于 "name" 是 `Mock` 构造器的参数之一，如果你想让你的 mock 对象具有 "name" 属性你不可以在创建时传入该参数。 有两个替代方式。 一个选项是使用 `configure_mock()`:

    >>> mock = MagicMock()
    >>> mock.configure_mock(name='my_name')
    >>> mock.name
    'my_name'

一个更简单的选项是在 mock 创建之后简单地设置 "name" 属性:

    >>> mock = MagicMock()
    >>> mock.name = "foo"

### 附加 Mock 作为属性

当你附加一个 mock 作为另一个 mock 的属性（或作为返回值）时它会成为该 mock 的 "子对象"。 对子对象的调用会被记录在父对象的 `method_calls` 和 `mock_calls` 属性中。 这适用于配置子 mock 然后将它们附加到父对象，或是将 mock 附加到将记录所有对子对象的调用的父对象上并允许你创建有关 mock 之间的调用顺序的断言:

    >>> parent = MagicMock()
    >>> child1 = MagicMock(return_value=None)
    >>> child2 = MagicMock(return_value=None)
    >>> parent.child1 = child1
    >>> parent.child2 = child2
    >>> child1(1)
    >>> child2(2)
    >>> parent.mock_calls
    [call.child1(1), call.child2(2)]

这里有一个例外情况是如果 mock 设置了名称。 这允许你在出于某些理由不希望其发生时避免 "父对象" 的影响。

    >>> mock = MagicMock()
    >>> not_a_child = MagicMock(name='not-a-child')
    >>> mock.attribute = not_a_child
    >>> mock.attribute()
    <MagicMock name='not-a-child()' id='...'>
    >>> mock.mock_calls
    []

通过 `patch()` 创建的 mock 会被自动赋予名称。 要将具有名称的 mock 附加到父对象上你应当使用 `attach_mock()` 方法:

    >>> thing1 = object()
    >>> thing2 = object()
    >>> parent = MagicMock()
    >>> with patch('__main__.thing1', return_value=None) as child1:
    ...     with patch('__main__.thing2', return_value=None) as child2:
    ...         parent.attach_mock(child1, 'child1')
    ...         parent.attach_mock(child2, 'child2')
    ...         child1('one')
    ...         child2('two')
    ...
    >>> parent.mock_calls
    [call.child1('one'), call.child2('two')]

1

  仅有的例外是魔术方法和属性（其名称前后都带有双下划线）。 Mock 不会创建它们而是将引发 `AttributeError`。 这是因为解释器将会经常隐式地请求这些方法，并且在它准备接受一个魔术方法却得到一个新的 Mock 对象时会 相当 困惑。 如果你需要魔术方法支持请参阅 魔术方法。

## patch 装饰器

patch 装饰器仅被用于在它们所装饰的函数作用域内部为对象添加补丁。 它们会自动为你执行去除补丁的处理，即使是在引发了异常的情况下。 所有这些函数都还可在 with 语句中使用或是作为类装饰器。

### patch

注解

问题的关键是要在正确的命名空间中打补丁。 参见 where to patch 一节。

`unittest.mock.``patch`(target, new=DEFAULT, spec=None, create=False, spec_set=None, autospec=None, new_callable=None, **kwargs)

  `patch()` 可以作为函数装饰器、类装饰器或上下文管理器。 在函数或 with 语句的内部，target 会打上一个 new 对象补丁。 当函数/with 语句退出时补丁将被撤销。

  如果 new 被省略，那么如果被打补丁的对象是一个异步函数则 target 将被替换为 `AsyncMock` 否则替换为 `MagicMock`。 如果 `patch()` 被用作装饰器并且 new 被省略，那么已创建的 mock 将作为一个附加参数传入被装饰的函数。 如果 `patch()` 被用作上下文管理器那么已创建的 mock 将被该上下文管理器所返回。is returned by the context manager.

  target 应当为 `'package.module.ClassName'` 形式的字符串。 target 将被导入并且该指定对象会被替换为 new 对象，因此 target 必须是可以从你调用 `patch()` 的环境中导入的。 target 会在被装饰的函数被执行的时候被导入，而非在装饰的时候。

  spec 和 spec_set 关键字参数会被传递给 `MagicMock`，如果 patch 为你创建了此对象的话。

  此外你还可以传入 `spec=True` 或 `spec_set=True`，这将使 patch 将被模拟的对象作为 spec/spec_set 对象传入。

  new_callable 允许你指定一个不同的类，或者可调用对象，它将被调用以创建 新的 对象。 在默认情况下将指定 `AsyncMock` 用于异步函数，`MagicMock` 用于其他函数。

  另一种更强形式的 spec 是 autospec。 如果你设置了 `autospec=True` 则将以来自被替换对象的 spec 来创建 mock。 mock 的所有属性也将具有被替换对象相应属性的 spec。 被模拟的方法和函数将检查它们的参数并且如果使用了错误的签名调用它们则将引发 `TypeError`。 对于替换了一个类的 mock，它们的返回值（即‘实例’）将具有与该类相同的 spec。 请参阅 `create_autospec()` 函数以及 Autospeccing。

  除了 `autospec=True` 你还可以传入 `autospec=some_object` 以使用任意对象而不是被替换的对象作为 spec。

  在默认情况下 `patch()` 将无法替换不存在的属性。 如果你传入 `create=True`，且该属性并不存在，则 patch 将在调用被打补丁的函数时为你创建该属性，并在退出被打补丁的函数时再次删除它。 这适用于编写针对生产代码在运行时创建的属性的测试。 它默认是被关闭的因为这具有危险性。 当它被开启时你将能够针对实际上并不存在的 API 编写通过测试！

  注解

  在 3.5 版更改: 如果你要给某个模块的内置函数打补丁则不必传入 `create=True`，它默认就会被添加。

  Patch 可以被用作 `TestCase` 类装饰器。 其作用是装饰类中的每个测试方法。 当你的测试方法共享同一个补丁集时这将减少模板代码。 `patch()` 会通过查找以 `patch.TEST_PREFIX` 打头的名称来找到测试。 其默认值为 `'test'`，这与 `unittest` 打到测试的方式一致。 你可以通过设置 `patch.TEST_PREFIX` 来指定其他的前缀。

  Patch 可以通过 with 语句作为上下文管理器使用。 这时补丁将应用于 with 语句的缩进代码块。 如果你使用了 "as" 则打补丁的对象将被绑定到 "as" 之后的名称；这非常适用于当 `patch()` 为你创建 mock 对象的情况。

  `patch()` 可接受任意关键字参数。 如果打补丁的对象是异步的则这些参数将被传给 `AsyncMock`，否则传给 `MagicMock`，或者是指定的 new_callable。

  `patch.dict(...)`, `patch.multiple(...)` 和 `patch.object(...)` 可用于其他使用场景。

`patch()` 作为函数装饰器，为你创建 mock 并将其传入被装饰的函数:

    >>> @patch('__main__.SomeClass')
    ... def function(normal_argument, mock_class):
    ...     print(mock_class is SomeClass)
    ...
    >>> function(None)
    True

为类打补丁将把该类替换为 `MagicMock` 的 实例。 如果该类是在受测试的代码中被实例化的则它将为所要使用的 mock 的 `return_value`。

如果该类被多次实例化则你可以使用 `side_effect` 来每次返回一个新 mock。 或者你也可以将 return_value 设为你希望的任何对象。

要在被打补丁的类的 实例 的方法上配置返回值你必须在 `return_value` 操作。 例如:

    >>> class Class:
    ...     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'
    ...

如果你使用 spec 或 spec_set 并且 `patch()` 替换的是 class，那么所创建的 mock 的返回值将具有同样的 spec。

    >>> Original = Class
    >>> patcher = patch('__main__.Class', spec=True)
    >>> MockClass = patcher.start()
    >>> instance = MockClass()
    >>> assert isinstance(instance, Original)
    >>> patcher.stop()

new_callable 参数适用于当你想要使用其他类来替代所创建的 mock 默认的 `MagicMock` 的场合。 例如，如果你想要使用 `NonCallableMock`:

    >>> 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

另一个使用场景是用 `io.StringIO` 实例来替换某个对象:

    >>> from io import StringIO
    >>> def foo():
    ...     print('Something')
    ...
    >>> @patch('sys.stdout', new_callable=StringIO)
    ... def test(mock_stdout):
    ...     foo()
    ...     assert mock_stdout.getvalue() == 'Something\n'
    ...
    >>> test()

当 `patch()` 为你创建 mock 时，通常你需要做的第一件事就是配置该 mock。 某些配置可以在对 patch 的调用中完成。 你在调用时传入的任何关键字参数都将被用来在所创建的 mock 上设置属性:

    >>> patcher = patch('__main__.thing', first='one', second='two')
    >>> mock_thing = patcher.start()
    >>> mock_thing.first
    'one'
    >>> mock_thing.second
    'two'

除了所创建的 mock 的属性上的属性，例如 `return_value` 和 `side_effect`，还可以配置子 mock 的属性。 将这些属性直接作为关键字参数传入在语义上是无效的，但是仍然能够使用 `**` 将以这些属性为键的字典扩展至一个 `patch()` 调用中

    >>> 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

在默认情况下，尝试给某个模块中并不存在的函数（或者某个类中的方法或属性）打补丁将会失败并引发 `AttributeError`:

    >>> @patch('sys.non_existing_attribute', 42)
    ... def test():
    ...     assert sys.non_existing_attribute == 42
    ...
    >>> test()
    Traceback (most recent call last):
      ...
    AttributeError: <module 'sys' (built-in)> does not have the attribute 'non_existing_attribute'

但在对 `patch()` 的调用中添加 `create=True` 将使之前示例的效果符合预期:

    >>> @patch('sys.non_existing_attribute', 42, create=True)
    ... def test(mock_stdout):
    ...     assert sys.non_existing_attribute == 42
    ...
    >>> test()

在 3.8 版更改: 如果目标为异步函数那么 `patch()` 现在将返回一个 `AsyncMock`。

### patch.object

`patch.``object`(target, attribute, new=DEFAULT, spec=None, create=False, spec_set=None, autospec=None, new_callable=None, **kwargs)

  用一个 mock 对象为对象 (target) 中指定名称的成员 (attribute) 打补丁。

  `patch.object()` 可以被用作装饰器、类装饰器或上下文管理器。 new, spec, create, spec_set, autospec 和 new_callable 等参数的含义与 `patch()` 的相同。 与 `patch()` 类似，`patch.object()` 接受任意关键字参数用于配置它所创建的 mock 对象。

  当用作类装饰器时 `patch.object()` 将认可 `patch.TEST_PREFIX` 作为选择所要包装方法的标准。

你可以附带三个参数或两个参数来调用 `patch.object()`。 三个参数的形式将接受要打补丁的对象、属性的名称以及将要替换该属性的对象。

将附带两个参数的形式调用时你将省略替换对象，还会为你创建一个 mock 并作为附加参数传入被装饰的函数:

    >>> @patch.object(SomeClass, 'class_method')
    ... def test(mock_method):
    ...     SomeClass.class_method(3)
    ...     mock_method.assert_called_with(3)
    ...
    >>> test()

传给 `patch.object()` 的 spec, create 和其他参数的含义与 `patch()` 的同名参数相同。

### patch.dict

`patch.``dict`(in_dict, values=(), clear=False, **kwargs)

  为一个目录或目录类对象打补丁，并在测试之后将该目录恢复到其初始状态。

  in_dict 可以是一个字典或映射类容器。 如果它是一个映射则它必须至少支持获取、设置和删除条目以及对键执行迭代。

  in_dict 也可以是一个指定字典名称的字符串，然后将通过导入操作来获取该字典。

  values 可以是一个要在字典中设置的值的字典。 values 也可以是一个包含 `(key, value)` 对的可迭代对象。

  如果 clear 为真值则该字典将在设置新值之前先被清空。

  `patch.dict()` 也可以附带任意关键字参数调用以设置字典中的值。

  在 3.8 版更改: 现在当 `patch.dict()` 被用作上下文管理器时将返回被打补丁的字典。now returns the patched dictionary when used as a context manager.

`patch.dict()` 可被用作上下文管理器、装饰器或类装饰器:

    >>> foo = {}
    >>> @patch.dict(foo, {'newkey': 'newvalue'})
    ... def test():
    ...     assert foo == {'newkey': 'newvalue'}
    >>> test()
    >>> assert foo == {}

当被用作类装饰器时 `patch.dict()` 将认可 `patch.TEST_PREFIX` (默认值为 `'test'`) 作为选择所在包装方法的标准:

    >>> import os
    >>> import unittest
    >>> from unittest.mock import patch
    >>> @patch.dict('os.environ', {'newkey': 'newvalue'})
    ... class TestSample(unittest.TestCase):
    ...     def test_sample(self):
    ...         self.assertEqual(os.environ['newkey'], 'newvalue')

如果你在为你的测试使用不同的前缀，你可以通过设置 `patch.TEST_PREFIX` 来将不同的前缀告知打补丁方。 有关如何修改该值的详情请参阅 TEST_PREFIX。

`patch.dict()` 可被用来向一个字典添加成员，或者简单地让测试修改一个字典，并确保当测试结束时恢复该字典。

    >>> foo = {}
    >>> with patch.dict(foo, {'newkey': 'newvalue'}) as patched_foo:
    ...     assert foo == {'newkey': 'newvalue'}
    ...     assert patched_foo == {'newkey': 'newvalue'}
    ...     # You can add, update or delete keys of foo (or patched_foo, it's the same dict)
    ...     patched_foo['spam'] = 'eggs'
    ...
    >>> assert foo == {}
    >>> assert patched_foo == {}

    >>> import os
    >>> with patch.dict('os.environ', {'newkey': 'newvalue'}):
    ...     print(os.environ['newkey'])
    ...
    newvalue
    >>> assert 'newkey' not in os.environ

可以在 `patch.dict()` 调用中使用关键字来设置字典的值:

    >>> mymodule = MagicMock()
    >>> mymodule.function.return_value = 'fish'
    >>> with patch.dict('sys.modules', mymodule=mymodule):
    ...     import mymodule
    ...     mymodule.function('some', 'args')
    ...
    'fish'

`patch.dict()` 可以用于实际上不是字典的字典类对象。 它们最少必须支持条目获取、设置、删除以及迭代或成员检测两者中的一个。 这对应于魔术方法 `__getitem__()`, `__setitem__()`, `__delitem__()` 以及 `__iter__()` 或 `__contains__()`。

    >>> class Container:
    ...     def __init__(self):
    ...         self.values = {}
    ...     def __getitem__(self, name):
    ...         return self.values[name]
    ...     def __setitem__(self, name, value):
    ...         self.values[name] = value
    ...     def __delitem__(self, name):
    ...         del self.values[name]
    ...     def __iter__(self):
    ...         return iter(self.values)
    ...
    >>> 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

`patch.``multiple`(target, spec=None, create=False, spec_set=None, autospec=None, new_callable=None, **kwargs)

  在单个调用中执行多重补丁。 它接受要打补丁的对象（一个对象或一个通过导入来获取对象的字符串）以及用于补丁的关键字参数:

      with patch.multiple(settings, FIRST_PATCH='one', SECOND_PATCH='two'):
          ...

  如果你希望 `patch.multiple()` 为你创建 mock 则要使用 `DEFAULT` 作为值。 在此情况下所创建的 mock 会通过关键字参数传入被装饰的函数，而当 `patch.multiple()` 被用作上下文管理器时则将返回一个字典。

  `patch.multiple()` 可以被用作装饰器、类装饰器或上下文管理器。 spec, spec_set, create, autospec 和 new_callable 等参数的含义与 `patch()` 的相同。 这些参数将被应用到 `patch.multiple()` 所打的 所有 补丁。

  当被用作类装饰器时 `patch.multiple()` 将认可 `patch.TEST_PREFIX` 作为选择所要包装方法的标准。

如果你希望 `patch.multiple()` 为你创建 mock，那么你可以使用 `DEFAULT` 作为值。 如果你使用 `patch.multiple()` 作为装饰器则所创建的 mock 会作为关键字参数传入被装饰的函数。

    >>> 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()` 可以与其他 `patch` 装饰器嵌套使用，但要将作为关键字传入的参数要放在 `patch()` 所创建的标准参数 之后:

    >>> @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 manager 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
    ...

### 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(unittest.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()

警告

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. `unittest.TestCase.addCleanup()` makes this easier:

    >>> class MyTest(unittest.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.

It is also possible to stop all patches which have been started by using `patch.stopall()`.

`patch.``stopall`()

  Stop all active patches. Only stops patches started with `start`.

### patch builtins

You can patch any builtins within a module. The following example patches builtin `ord()`:

    >>> @patch('__main__.ord')
    ... def test(mock_ord):
    ...     mock_ord.return_value = 101
    ...     print(ord('c'))
    ...
    >>> test()
    101

### 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 `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:
    ...     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

`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 in the 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 settings object.

## MagicMock and magic method support

### Mocking Magic Methods

`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 2, 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 3.

    >>> 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 `method_calls`, but they are recorded in `mock_calls`.

注解

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__`

- `__round__`, `__floor__`, `__trunc__` and `__ceil__`

- Comparisons: `__lt__`, `__gt__`, `__le__`, `__ge__`, `__eq__` and `__ne__`

- Container methods: `__getitem__`, `__setitem__`, `__delitem__`, `__contains__`, `__len__`, `__iter__`, `__reversed__` and `__missing__`

- Context manager: `__enter__`, `__exit__`, `__aenter__` and `__aexit__`

- Unary numeric methods: `__neg__`, `__pos__` and `__invert__`

- The numeric methods (including right hand and in-place variants): `__add__`, `__sub__`, `__mul__`, `__matmul__`, `__div__`, `__truediv__`, `__floordiv__`, `__mod__`, `__divmod__`, `__lshift__`, `__rshift__`, `__and__`, `__xor__`, `__or__`, and `__pow__`

- Numeric conversion methods: `__complex__`, `__int__`, `__float__` and `__index__`

- Descriptor methods: `__get__`, `__set__` and `__delete__`

- Pickling: `__reduce__`, `__reduce_ex__`, `__getinitargs__`, `__getnewargs__`, `__getstate__` and `__setstate__`

- File system path representation: `__fspath__`

- Asynchronous iteration methods: `__aiter__` and `__anext__`

在 3.8 版更改: Added support for `os.PathLike.__fspath__()`.

在 3.8 版更改: Added support for `__aenter__`, `__aexit__`, `__aiter__` and `__anext__`.

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 `unittest.mock.``MagicMock`(*args, **kw)

  `MagicMock` is a subclass of `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 `Mock`.

  If you use the spec or spec_set arguments then only magic methods that exist in the spec will be created.

class `unittest.mock.``NonCallableMagicMock`(*args, **kw)

  A non-callable version of `MagicMock`.

  The constructor parameters have the same meaning as for `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__`: `0`

- `__iter__`: `iter([])`

- `__exit__`: `False`

- `__aexit__`: `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

例如:

    >>> mock = MagicMock()
    >>> int(mock)
    1
    >>> len(mock)
    0
    >>> list(mock)
    []
    >>> object() in mock
    False

The two equality methods, `__eq__()` and `__ne__()`, are special. They do the default equality comparison on identity, using the `side_effect` attribute, 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__`

2

  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.

3

  The function is basically hooked up to the class, but each `Mock` instance is kept isolated from the others.

## Helpers

### sentinel

`unittest.mock.``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.

  在 3.7 版更改: The `sentinel` attributes now preserve their identity when they are `copied` or `pickled`.

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
    >>> result
    sentinel.some_object

### DEFAULT

`unittest.mock.``DEFAULT`

  The `DEFAULT` object is a pre-created sentinel (actually `sentinel.DEFAULT`). It can be used by `side_effect` functions to indicate that the normal return value should be used.

### call

`unittest.mock.``call`(*args, **kwargs)

  `call()` is a helper object for making simpler assertions, for comparing with `call_args`, `call_args_list`, `mock_calls` and `method_calls`. `call()` can also be used with `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

`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 `mock_calls` on a mock. Manually constructing the sequence of calls can be tedious.

`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

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 `Mock.call_args`, `Mock.call_args_list` and `Mock.mock_calls` attributes can be introspected to get at the individual arguments they contain.

The `call` objects in `Mock.call_args` and `Mock.call_args_list` are two-tuples of (positional args, keyword args) whereas the `call` objects in `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
    >>> kall.args
    (1, 2, 3)
    >>> kall.kwargs
    {'arg': 'one', 'arg2': 'two'}
    >>> kall.args is kall[0]
    True
    >>> kall.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
    {'arg': 'two', 'arg2': 'three'}
    >>> name is m.mock_calls[0][0]
    True

### create_autospec

`unittest.mock.``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 Autospeccing for examples of how to use auto-speccing with `create_autospec()` and the autospec argument to `patch()`.

在 3.8 版更改: `create_autospec()` now returns an `AsyncMock` if the target is an async function.

### ANY

`unittest.mock.``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 `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 `assert_called_with()` and `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 `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

`unittest.mock.``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',
     'assert_called_once',
     'assert_called_once_with',
     'assert_called_with',
     'assert_has_calls',
     'assert_not_called',
     '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

`unittest.mock.``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()`, `readline()`, and `readlines()` methods of the file handle to return. Calls to those methods will take data from read_data until it is depleted. The mock of these methods is pretty simplistic: every time the mock is called, the read_data is rewound to the start. If you need more control over the data that you are feeding to the tested code you will need to customize this mock for yourself. When that is insufficient, one of the in-memory filesystem packages on PyPI can offer a realistic filesystem for testing.

  在 3.4 版更改: Added `readline()` and `readlines()` support. The mock of `read()` changed to consume read_data rather than returning it on each call.

  在 3.5 版更改: read_data is now reset on each call to the mock.

  在 3.8 版更改: Added `__iter__()` to implementation so that iteration (such as in for loops) correctly consumes read_data.

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 `MagicMock` is common enough and fiddly enough that a helper function is useful.

    >>> m = mock_open()
    >>> with patch('__main__.open', m):
    ...     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')) as m:
    ...     with open('foo') as h:
    ...         result = h.read()
    ...
    >>> m.assert_called_once_with('foo')
    >>> assert result == 'bibble'

### 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: `assert_called_with()` and `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 'mock' 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:

    >>> mock = Mock(name='Thing', return_value=None)
    >>> mock(1, 2, 3)
    >>> mock.assret_called_once_with(4, 5, 6)  # Intentional typo!

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  # Intentional typo!
    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:

    >>> mock.has_data()
    <mock.Mock object at 0x...>
    >>> mock.has_data.assret_called_with()  # Intentional typo!

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  # Intentional typo!
    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 `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 4.

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:
    ...   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.

    class Something:
        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:
    ...     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:
    ...   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='...'>

4

  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.

### Sealing mocks

`unittest.mock.``seal`(mock)

  Seal will disable the automatic creation of mocks when accessing an attribute of the mock being sealed or any of its attributes that are already mocks recursively.

  If a mock instance with a name or a spec is assigned to an attribute it won't be considered in the sealing chain. This allows one to prevent seal from fixing part of the mock object.

      >>> mock = Mock()
      >>> mock.submock.attribute1 = 2
      >>> mock.not_submock = mock.Mock(name="sample_name")
      >>> seal(mock)
      >>> mock.new_attribute  # This will raise AttributeError.
      >>> mock.submock.attribute2  # This will raise AttributeError.
      >>> mock.not_submock.attribute2  # This won't raise.

  3.7 新版功能.