async_mock_or_lambda.py

class EventDispatcher:
    def __init__(self, loop, input_handler, output_handler):
        self.loop = loop
        self.input_handler = input_handler
        self.output_handler = output_handler

    async def __call__(self, event):
        # Generic stuff (logging, benchmarking, ...)
        message = await self.input_handler(event)
        await self.output_handler(message)



# Current and only way to test if the input handler gets called:
@pytest.mark.asyncio
async def test_calls_input_handler(loop):
    async def input_handler(event):
        input_handler.called = True

    async def output_handler(_):
        pass

    dispatcher = EventDispatcher(input_handler, output_handler)
    await dispatcher('abc')

    assert input_handler.called is True


# What I would prefer:
@pytest.mark.asyncio
async def test_calls_input_handler(loop):
    from unittest.mock import AsyncMock

    input_handler = AsyncMock()
    
    dispatcher = EventDispatcher(input_handler, AsyncMock())
    await dispatcher('abc')

    assert input_handler.called is True


# Or even:
@pytest.mark.asyncio
async def test_calls_input_handler(loop):
    async def input_handler(event):
        input_handler.called = True

    output_handler = async lambda: None

    dispatcher = EventDispatcher(input_handler, output_handler)
    await dispatcher('abc')

    assert input_handler.called is True