test passes but ERROR is thrown when closing a generator, only shows up in pytest-asyncio pytest run

[jreiberkyle]

I am running python 3.7.9 and pytest-asyncio 0.14.0 / pytest 6.2.1. When I run the following code in pytest, I get an error thrown even though the test passes.

$>pytest -vv test.py --log-cli-level=DEBUG

test.py

import pytest
@pytest.mark.asyncio
async def test_generator_limit():
    async def gen():
        yield 1
        yield 2
        yield 3
        yield 4

    async for res in gen():
        if res == 2:
            break

ERROR asyncio:base_events.py:1619 Task was destroyed but it is pending! task: <Task pending coro=<<async_generator_athrow without __name__>()>>

If I run this code as a script, I get no such error

import asyncio

async def test_generator_limit():
    async def gen():
        yield 1
        yield 2
        yield 3
        yield 4

    async for res in gen():
        if res == 2:
            break

asyncio.run(test_generator_limit(), debug=True)

(NOTE: the value of debug does not change the results)

This error only shows up when I introduce the break. According to PEP 525 this appears to be valid async code.

[seifertm]

Thanks for the report and for the great examples! The issue is still present in pytest-async v0.16.

asyncio.run cleans up any async generator functions before exiting (see #222). This is why you don't see the "Task pending error" when running your second example. pytest-asyncio does no such thing when the event_loop fixture is torn down, resulting in the error you describe.

Issue #222 proposed that pytest-asyncio should behave similar to asyncio.run and clean up existing tasks. We closed that in favour of #235. I hope you don't mind if I do the same here. Let's continue the discussion in #235.