Python 模拟 return 初始预定义值后的默认值 returned

Question

我正在模拟一个消息队列，我希望它在每次调用时 return 2 条消息然后 return None （模拟消息队列是现在是空的）。但是，在第三次消息调用之后，我从模拟框架中收到一条错误消息，指出没有 "next" 值。

这是一个例子：

from mock import MagicMock

mock_message_queue = MagicMock(name='message_queue')
expected_messages = ['message 1', 'message 2', None]
mock_message_queue.fetch.side_effect = expected_messages

print('mock_message_queue.fetch() = {}'.format(mock_message_queue.fetch()))
print('mock_message_queue.fetch() = {}'.format(mock_message_queue.fetch()))
print('mock_message_queue.fetch() = {}'.format(mock_message_queue.fetch()))
print('mock_message_queue.fetch() = {}'.format(mock_message_queue.fetch()))

输出：

mock_message_queue.fetch() = message 1
mock_message_queue.fetch() = message 2
mock_message_queue.fetch() = None
Traceback (most recent call last):
  File "/home/wsi/.PyCharm2017.1/config/scratches/mock_message_bus.py", line 10, in <module>
    print('mock_message_queue.fetch() = {}'.format(mock_message_queue.fetch()))
  File "/usr/local/lib/python3.5/dist-packages/mock/mock.py", line 1062, in __call__
    return _mock_self._mock_call(*args, **kwargs)
  File "/usr/local/lib/python3.5/dist-packages/mock/mock.py", line 1121, in _mock_call
    result = next(effect)
StopIteration

Process finished with exit code 1

所以基本上我希望它总是 return None 在它 returns 'message 2' 之后。有人知道怎么做吗？

Answer 1

问题是您需要值列表的最后一个元素无限重复。您可以为此使用 itertools.repeat，并使用 itertools.chain 将其加入实际值列表。

expected_messages = itertools.chain(['message 1', 'message 2'], itertools.repeat(None))

Python 模拟 return 初始预定义值后的默认值 returned

Python mock return default value after initial predefined values returned

python

unit-testing

mocking

python-mock