将mock.patch的autospec选项与自定义Mock子类一起使用

Question

我正在尝试使用（反向移植）模块将间谍附加到类中的方法mock。也就是说，我想创建一个模拟，其工作原理与原始方法类似，但提供常用Mock功能call_count，例如等。

这是我当前使用的代码：

import mock

class MyClass(object):
    def my_method(self, arg):
        return arg + 1

def unit_under_test():
    inst = MyClass()
    return inst.my_method(1)

with mock.patch.object(MyClass, 'my_method', autospec=True,
                       side_effect=MyClass.my_method) as spy:
    result = unit_under_test()
    assert result == 2
    assert spy.call_count == 1

效果很好。现在我想使用 的自定义子类MagicMock来代替。文档说这可以通过参数patch来new_callable完成。但是，new_callable和autospec不能一起使用：

class MyMock(mock.MagicMock):
    pass

with mock.patch.object(MyClass, 'my_method', autospec=True,
                       side_effect=MyClass.my_method,
                       new_callable=MyMock) as spy:
    ...

Traceback (most recent call last):
  File "./mocktest.py", line 19, in <module>
    new_callable=MyMock) as spy:
  File "/var/foo/venv/local/lib/python2.7/site-packages/mock.py", line 1442, in _patch_object
    spec_set, autospec, new_callable, kwargs
  File "/var/foo/venv/local/lib/python2.7/site-packages/mock.py", line 1127, in __init__
    "Cannot use 'autospec' and 'new_callable' together"
ValueError: Cannot use 'autospec' and 'new_callable' together

问题是省略autospec也不起作用，因为 thenself没有传递给原始方法：

with mock.patch.object(MyClass, 'my_method',
                       side_effect=MyClass.my_method,
                       new_callable=MyMock) as spy:
    ...

Traceback (most recent call last):
  File "./mocktest.py", line 20, in <module>
    result = unit_under_test()
  File "./mocktest.py", line 11, in unit_under_test
    return inst.my_method(1)
  File "/var/foo/venv/local/lib/python2.7/site-packages/mock.py", line 955, in __call__
    return _mock_self._mock_call(*args, **kwargs)
  File "/var/foo/venv/local/lib/python2.7/site-packages/mock.py", line 1018, in _mock_call
    ret_val = effect(*args, **kwargs)
TypeError: unbound method my_method() must be called with MyClass instance as first argument (got int instance instead)

请注意，我无法修补my_method实例，因为我正在测试的MyClass 代码创建了自己的MyClass实例（如上面的示例代码所示）。

Answer 1

这里的问题是在设置时mock.py 硬编码 MagicMock为模拟类。autospec

一个简单的解决方法是用MagicMock你自己的补丁来修补自己：

with mock.patch.object(mock, 'MagicMock', MyMock):
    with mock.patch.object(MyClass, 'my_method', autospec=True,
                           side_effect=MyClass.my_method) as spy:
        ...

演示： https: //ideone.com/iPMnSc