我对AsyncIO很陌生，希望能得到一些帮助。我有一个运行聚合管道的基本类，它在生产中运行得很好：

class BasePipeline2:
    client: motor.AsyncIOMotorClient
    db: motor.AsyncIOMotorDatabase
    collection: motor.AsyncIOMotorCollection

    def __init__(self, uri: str, database: str, collection: str):
        self.client = get_client(uri)
        self.db = self.client[database]
        self.collection = self.db[collection]

    async def run(self):
        """Runs the pipeline and returns the results as a list"""
        result = await self.collection.aggregate({"$match": {"foo": "bar"}}).to_list(length=None)
        return result

我介绍了以下测试：

@pytest.mark.asyncio
async def test_run2(self):
    results = [{"_id": 1, "name": "Alice", "age": 25}, {"_id": 2, "name": "Bob", "age": 30}]
    cursor_mock = mock.AsyncMock()
    cursor_mock.to_list = mock.AsyncMock(return_value=results)

    collection_mock = mock.MagicMock()
    collection_mock.aggregate = mock.AsyncMock(return_value=cursor_mock)

    pipeline = BasePipeline2("mongodb://localhost:27017/", "test_db", "test_collection")
    with mock.patch.object(pipeline, "collection", collection_mock):
        pipeline_result = await pipeline.run()

    assert pipeline_result == results

我试图模拟to_list方法来返回测试结果。然而，无论我怎么尝试，我都会得到一个错误：

AttributeError: 'coroutine' object has no attribute 'to_list'

我似乎找不到解决方案，我觉得问题出在我设置模拟的方式上。