如何模拟 "async with" 语句？

Question

我正在尝试为使用“async with”语句（在本例中为 aioredis 的连接池）的方法编写测试，我想模拟与 redis 的连接，但我无法弄清楚如何.

这是我目前的情况：

from asyncio import Future
from unittest.mock import MagicMock

import pytest

# The thing i'm trying to test
async def set_value(redis, value):
    # Do things
    async with redis.get() as conn:
        await conn.set("key", value)

#My Mock classes
class MockRedis():
    def get(self):
        return MockAsyncPool()


class MockAsyncPool(MagicMock):
    async def __aenter__(self):
        conn = MagicMock()
        f = Future()
        f.set_result(True)
        conn.set = MagicMock(return_value=f)
        return conn

    def __aexit__(self, exc_type, exc_val, exc_tb):
        pass


# The actual test
@pytest.mark.asyncio
async def test_get_token():
    redis = MockRedis()

    token = await set_value(redis, 'something')
    assert token is not None

我运行它与：

py.test path/to/file.py

我收到这个错误：

> await conn.set("key", value)

E TypeError: object NoneType can't be used in 'await' expression

Answer 1

__aexit__ 也需要异步 (needs to return an awaitable):

async def __aexit__(self, exc_type, exc_val, exc_tb):
    pass

如果不是异步，它会返回 None 而不是协程，因此它会引发错误，至于我创建的非常具有误导性的错误消息 this issue 以指出错误消息需要固定。

如何模拟 "async with" 语句？

How to mock "async with" statements?

mocking

pytest

python-3.x

python-asyncio