python - 如何让 mock.mock_open 引发 IOError？

Question

我需要测试调用open 的实例方法。在第一个测试用例中，我将 mock.mock_open 设置为按预期返回一个字符串。这非常有效。

但是，我还需要测试从该函数中抛出 IOError 的情况。如何让 mock.mock_open 引发任意异常？

到目前为止，这是我的方法:

@mock.patch.object(somemodule, 'generateDefaultKey')
def test_load_privatekey(self, genkey)
    mo = mock.mock_open(read_data=self.key)
    mo.side_effect = IOError
    with mock.patch('__main__.open', mo, create=True):
        self.controller.loadPrivkey()

    self.assertTrue(genkey.called, 'Key failed to regenerate')

Answer 1

将异常分配给mock.mock_open.side_effect:

mock.mock_open.side_effect = IOError

来自mock.Mock.side_effect documentation :

This can either be a function to be called when the mock is called, or an exception (class or instance) to be raised.

演示:

>>> mock = MagicMock()
>>> mock.mock_open.side_effect = IOError()
>>> mock.mock_open()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/mj/Development/venvs/stackoverflow-2.7/lib/python2.7/site-packages/mock.py", line 955, in __call__
    return _mock_self._mock_call(*args, **kwargs)
  File "/Users/mj/Development/venvs/stackoverflow-2.7/lib/python2.7/site-packages/mock.py", line 1010, in _mock_call
    raise effect
IOError

当使用patch() 作为上下文管理器时，会生成一个新的模拟对象；分配给那个模拟对象:

with mock.patch('__main__.open', mo, create=True) as mocked_open:
    mocked_open.side_effect = IOError()
    self.controller.loadPrivkey()