RuntimeError: Cannot run the event loop while another loop is running

[baiyyee]

When trying to do UI automtion with pytest-asyncio and pytest-playwright, I got exception like: RuntimeError: Cannot run the event loop while another loop is running

Code structure:

ui2/conftest.py
ui2/test_bing.py

ui2/conftest.py

import pytest
import asyncio


@pytest.fixture(scope="session")
def event_loop():
    """重写event_loop"""

    loop = asyncio.get_event_loop()
    yield loop
    loop.close()

ui2/test_bing.py

import pytest

from playwright.async_api import Page


@pytest.mark.asyncio
async def test_bing(page: Page):
    await page.goto("http://www.bing.com")

env:

pytest==7.1.2
pytest-asyncio==0.18.3
pytest-playwright==0.3.0

Detail exception as below:

[seifertm]

Thank you for the report and the example. Unfortunately, I will not have time to look into this for the next two weeks. If nobody else is going to pick this up, it'll have to wait until then.

[PeterStolz]

Hi, I also encountered a similar problem.
To give you a minimal proof of concept in python3.10:
runner.py

import pytest                                                                                                   
import asyncio                                                                                                  
                 
# using nest_asyncio mitigates the problem                                                                                               
#import nest_asyncio                                                                                            
#nest_asyncio.apply()                                                                                                      
                                                                                                                
async def runner():                                                                                             
    pytest.main(['-k', 'test_asdf', 'test_file.py'])                                                            
                                                                                                                
loop = asyncio.get_event_loop()                                                                                 
loop.run_until_complete(runner())                                                                               
           
# does not raise an exception                                                                                                                                                                                                                     
# pytest.main(['-k', 'test_asdf', 'test_file.py'])     

test_file.py

import pytest                                                                                                   
                                                                                                                
@pytest.mark.asyncio                                                                                            
async def test_asdf():                                                                                          
    assert True     

Executing the runner yields the same stacktrace:

/home/peter/Documents/pytestbug/test_runner.py:14: DeprecationWarning: There is no current event loop
  loop = asyncio.get_event_loop()
============================================= test session starts ==============================================
platform linux -- Python 3.10.4, pytest-7.1.2, pluggy-1.0.0
rootdir: /home/peter/Documents/pytestbug
plugins: asyncio-0.18.4.dev36+gc021932.d20220609
asyncio: mode=legacy
collected 1 item                                                                                               

test_file.py F                                                                                           [100%]

=================================================== FAILURES ===================================================
__________________________________________________ test_asdf ___________________________________________________

args = (), kwargs = {}, coro = <coroutine object test_asdf at 0x7f7c47cb3300>
old_loop = <_UnixSelectorEventLoop running=False closed=False debug=False>
task = <Task pending name='Task-2' coro=<test_asdf() running at /home/peter/Documents/pytestbug/test_file.py:5>>

    @functools.wraps(func)
    def inner(*args, **kwargs):
        coro = func(*args, **kwargs)
        if not inspect.isawaitable(coro):
            pyfuncitem.warn(
                pytest.PytestWarning(
                    f"The test {pyfuncitem} is marked with '@pytest.mark.asyncio' "
                    "but it is not an async function. "
                    "Please remove asyncio marker. "
                    "If the test is not marked explicitly, "
                    "check for global markers applied via 'pytestmark'."
                )
            )
            return
        nonlocal _loop
        _loop.stop()
        old_loop = _loop
        # old_loop
        _loop = asyncio.new_event_loop()
        asyncio.set_event_loop(_loop)
        task = asyncio.ensure_future(coro, loop=_loop)
        try:
>           _loop.run_until_complete(task)

../../.virtualenvs/pytestbug/lib/python3.10/site-packages/pytest_asyncio/plugin.py:460: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
/usr/lib/python3.10/asyncio/base_events.py:622: in run_until_complete
    self._check_running()
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <_UnixSelectorEventLoop running=False closed=False debug=False>

    def _check_running(self):
        if self.is_running():
            raise RuntimeError('This event loop is already running')
        if events._get_running_loop() is not None:
>           raise RuntimeError(
                'Cannot run the event loop while another loop is running')
E           RuntimeError: Cannot run the event loop while another loop is running

/usr/lib/python3.10/asyncio/base_events.py:584: RuntimeError
=============================================== warnings summary ===============================================
../../.virtualenvs/pytestbug/lib/python3.10/site-packages/pytest_asyncio/plugin.py:191
  /home/peter/.virtualenvs/pytestbug/lib/python3.10/site-packages/pytest_asyncio/plugin.py:191: DeprecationWarning: The 'asyncio_mode' default value will change to 'strict' in future, please explicitly use 'asyncio_mode=strict' or 'asyncio_mode=auto' in pytest configuration file.
    config.issue_config_time_warning(LEGACY_MODE, stacklevel=2)

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
=========================================== short test summary info ============================================
FAILED test_file.py::test_asdf - RuntimeError: Cannot run the event loop while another loop is running
========================================= 1 failed, 1 warning in 0.10s =========================================
/usr/lib/python3.10/asyncio/base_events.py:685: ResourceWarning: unclosed event loop <_UnixSelectorEventLoop running=False closed=False debug=False>
sys:1: RuntimeWarning: coroutine 'test_asdf' was never awaited
Task was destroyed but it is pending!
task: <Task pending name='Task-2' coro=<test_asdf() running at /home/peter/Documents/pytestbug/test_file.py:5>>

The problem is that there is an existing event loop that is already running and I suspect that is happening on @SilenceHe 's imported code

This can be mitigated by using nest_asyncio.

I tried other solutions but unfortunately it seems like using nest_asyncio is the best option.

[graingert]

one issue here is that you're expecting an async_api.Page, but pytest-playright uses the sync_api.Page https://github.com/microsoft/playwright-pytest/blob/456f8286f09f132d2e21f6bf71f27465e71ba17a/pytest_playwright/pytest_playwright.py#L22

import pytest

from playwright.async_api import Page


@pytest.mark.asyncio
async def test_bing(page: Page):
    await page.goto("http://www.bing.com/")

[seifertm]

@graingert Thanks for jumping in!

As mentioned playwright-pytest only supports the synchronous Playwright API at the moment (see microsoft/playwright-pytest#74).

@SilenceHe This comment in particular state that only playwright.sync_api is supported by playwright-pytest and links to a conftest.py that allows the asynchronous API to be used.

[seifertm]

I didn't know about nest_asyncio. The project seems to solve the same problem as https://github.com/aio-libs/aioloop-proxy for which a draft PR exists (#312).

@PeterStolz Your error message is similar to that of the OP. I see your problem as a different one, though, because it has nothing to do with playwright-pytest. Do you mind opening a separate issue for your? It would be very helpful if you could explain your use case a bit more.

CC @asvetlov It seems that nest_asyncio and aioloop-proxy do pretty much the same.

[seifertm]

Closing this issue as this doesn't seem to be a pytest-asyncio bug. Feel free to reopen, especially if there is anything we can do to improve support for playwright-pytest.