Python asyncio：如何模拟__aiter __（）方法？

Question

我有一个代码，正在使用侦听WebSocket上的消息aiohttp。

看起来像：

async for msg in ws:
    await self._ws_msg_handler.handle_message(ws, msg, _services)

（原始代码）ws的实例在哪里aiohttp.web.WebSocketResponse()

在我的测试中，我模拟了WebSocketResponse()它及其__aiter__方法：

def coro_mock(**kwargs):
    return asyncio.coroutine(mock.Mock(**kwargs))


@pytest.mark.asyncio
@mock.patch('aiojsonrpc.request_handler.WebSocketMessageHandler')
async def test_rpc_websocket_handler(
    MockWebSocketMessageHandler,
    rpc_websocket_handler
):

    ws_response = 'aiojsonrpc.request_handler.WebSocketResponse'
    with mock.patch(ws_response) as MockWebSocketResponse:
        MockRequest = mock.MagicMock()
        req = MockRequest()

        ws_instance = MockWebSocketResponse.return_value
        ws_instance.prepare = coro_mock()
        ws_instance.__aiter__ = coro_mock(return_value=iter(range(5)))
        ws_instance.__anext__ = coro_mock()

        handle_msg_result = 'Message processed'
        MockWebSocketMessageHandler.handle_message.side_effect = Exception(
            handle_msg_result)
        msg_handler = MockWebSocketMessageHandler()

        with pytest.raises(Exception) as e:
            await request_handler.RpcWebsocketHandler(msg_handler)(req)
        assert str(e.value) == handle_msg_result

虽然当我运行测试时失败，并显示以下错误消息：

'async for'需要一个带有__aiter__方法的对象，得到了MagicMock

=================================================================================== FAILURES ===================================================================================
__________________________________________________________________________ test_rpc_websocket_handler __________________________________________________________________________

MockWebSocketMessageHandler = <MagicMock name='WebSocketMessageHandler' id='140687969989632'>
rpc_websocket_handler = <aiojsonrpc.request_handler.RpcWebsocketHandler object at 0x7ff47879b0f0>

    @pytest.mark.asyncio
    @mock.patch('aiojsonrpc.request_handler.WebSocketMessageHandler')
    async def test_rpc_websocket_handler(
        MockWebSocketMessageHandler,
        rpc_websocket_handler
    ):

        ws_response = 'aiojsonrpc.request_handler.WebSocketResponse'
        with mock.patch(ws_response) as MockWebSocketResponse:
            # MockRequest = mock.create_autospec(aiohttp.web_reqrep.Request)
            # req = MockRequest(*[None] * 6)
            MockRequest = mock.MagicMock()
            req = MockRequest()

            ws_instance = MockWebSocketResponse.return_value
            ret = mock.Mock()
            ws_instance.prepare = coro_mock()
            ws_instance.__aiter__ = coro_mock(return_value=iter(range(5)))
            ws_instance.__anext__ = coro_mock()

            handle_msg_result = 'Message processed'
            MockWebSocketMessageHandler.handle_message.side_effect = Exception(
                handle_msg_result)
            msg_handler = MockWebSocketMessageHandler()

            with pytest.raises(Exception) as e:
                await request_handler.RpcWebsocketHandler(msg_handler)(req)
>           assert str(e.value) == handle_msg_result
E           assert "'async for' ...got MagicMock" == 'Message processed'
E             - 'async for' requires an object with __aiter__ method, got MagicMock
E             + Message processed

tests/test_request_handler.py:252: AssertionError

因此，它的行为就像__aiter__()从来没有被嘲笑过。在这种情况下，我应该如何完成正确的模拟？

---

更新：

现在，我已经找到了一种解决方法，可以使代码可测试，但是如果有人告诉我如何处理原始问题中描述的问题，我将不胜感激。

Answer 1

适用于 py38

from unittest.mock import MagicMock

async def test_iterable(self):
    loop_iterations = 0
    mock = MagicMock()
    mock.__aiter__.return_value = range(5)
    async for _ in mock:
        loop_iterations += 1

    self.assertEqual(5, loop_iterations)

Answer 2

您可以使模拟类返回一个实现预期接口的对象：

class AsyncIterator:
    def __init__(self, seq):
        self.iter = iter(seq)

    async def __aiter__(self):
        return self

    async def __anext__(self):
        try:
            return next(self.iter)
        except StopIteration:
            raise StopAsyncIteration

MockWebSocketResponse.return_value = AsyncIterator(range(5))

我认为还没有一种方法可以正确模拟对象的实现__aiter__，它可能是python的bug，因为async for拒绝a MagicMock，即使hasattr(the_magic_mock, '__aiter__')是True。

编辑（13/12/2017）：自0.11起，asynctest库支持异步迭代器和上下文管理器asynctest.MagicMock免费提供此功能。

Answer 3

对于后代，我遇到了需要测试async for循环的相同问题，但已接受的解决方案似乎不适用于 Python 3.7。下面的示例适用于3.6.xand 3.7.0，但不适用于3.5.x：

import asyncio


class AsyncIter:    
    def __init__(self, items):    
        self.items = items    

    async def __aiter__(self):    
        for item in self.items:    
            yield item    


async def print_iter(items):
    async for item in items:
        print(item)


if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    things = AsyncIter([1, 2, 3])
    loop.run_until_complete(print_iter(things))
    loop.close()

有了上面的内容，嘲笑它看起来像：

with mock.patch('some.async.iter', return_value=AsyncIter([1, 2, 3])):
  # do test requiring mocked iter