pytest-asyncio RuntimeError: Cannot run the event loop while another loop is running

Question

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:

Answer 1

Short solution.

Install nest_asyncio:

pip install nest_asyncio

Then add this to your main conftest.py file:

import nest_asyncio
nest_asyncio.apply()

Find a more detailed explanation over here:

https://pypi.org/project/nest-asyncio/

Answer 2

Because you're importing from the async_api it sounds like you're writing asynchronous integration tests that you want to run concurrently. pytest-asyncio runs coroutine tests serially, so you instead want to use pytest-asyncio-cooperative. (If you wanted the tests run serially you should use from playwright.sync_api import Page.) I'd suggest:

1. Install pytest-asyncio-cooperative

pip install pytest-asyncio-cooperative

2. Remove event_loop fixture from ui2/conftest.py. pytest-asyncio-cooperative runs all test coroutines asynchronously on the same event loop implicitly.

3. Mark your async tests with @pytest.mark.asyncio_cooperative

import pytest

from playwright.async_api import Page


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

4. Run your tests with the -p no:asyncio option. pytest-aysncio is not compatible with pytest-asyncio-cooperative, so it has to be disabled or uninstalled.

pytest -p no:asyncio