[feat] Extend warning message about unclosed event loops with additio…

…nal possible cause.

Closes #531

Signed-off-by: Michael Seifert <m.seifert@digitalernachschub.de>

docs/source/reference/changelog.rst

@@ -5,6 +5,8 @@ Changelog
 0.22.0 (UNRELEASED)
 ===================
 - Output a proper error message when an invalid ``asyncio_mode`` is selected.
+- Extend warning message about unclosed event loops with additional possible cause.
+  `#531 <https://github.com/pytest-dev/pytest-asyncio/issues/531>`_
 
 0.21.0 (2023-03-19)
 ===================

pytest_asyncio/plugin.py

@@ -434,7 +434,8 @@ def _add_finalizers(fixturedef: FixtureDef, *finalizers: Callable[[], object]) -
     library will no longer do so. In order to ensure compatibility with future
     versions, please make sure that:
         1. Any custom "event_loop" fixture properly closes the loop after yielding it
-        2. Your code does not modify the event loop in async fixtures or tests
+        2. The scopes of your custom "event_loop" fixtures do not overlap
+        3. Your code does not modify the event loop in async fixtures or tests
     """
 )