[feat] Raises a MultipleEventLoopsRequested error when a function-scoped loop is pulled in by an async autouse fixture in addition to an event loop with larger scope.

Signed-off-by: Michael Seifert <[email protected]>

Author: seifertm

docs/source/reference/changelog.rst

@@ -5,6 +5,7 @@ Changelog
 0.23.8 (UNRELEASED)
 ===================
 - Fixes a bug that caused duplicate markers in async tests `#813 <https://github.com/pytest-dev/pytest-asyncio/issues/813>`_
+- Improves detection of multiple event loops being requested by the same test in strict mode `#868 <https://github.com/pytest-dev/pytest-asyncio/issues/868>`_
 
 Known issues
 ------------

pytest_asyncio/plugin.py

@@ -707,14 +707,6 @@ def pytest_generate_tests(metafunc: Metafunc) -> None:
     event_loop_fixture_id = event_loop_node.stash.get(_event_loop_fixture_id, None)
 
     if event_loop_fixture_id:
-        # This specific fixture name may already be in metafunc.argnames, if this
-        # test indirectly depends on the fixture. For example, this is the case
-        # when the test depends on an async fixture, both of which share the same
-        # event loop fixture mark.
-        if event_loop_fixture_id in metafunc.fixturenames:
-            return
-        fixturemanager = metafunc.config.pluginmanager.get_plugin("funcmanage")
-        assert fixturemanager is not None
         if "event_loop" in metafunc.fixturenames:
             raise MultipleEventLoopsRequestedError(
                 _MULTIPLE_LOOPS_REQUESTED_ERROR.format(
@@ -723,6 +715,14 @@ def pytest_generate_tests(metafunc: Metafunc) -> None:
                     scoped_loop_node=event_loop_node.nodeid,
                 ),
             )
+        # This specific fixture name may already be in metafunc.argnames, if this
+        # test indirectly depends on the fixture. For example, this is the case
+        # when the test depends on an async fixture, both of which share the same
+        # event loop fixture mark.
+        if event_loop_fixture_id in metafunc.fixturenames:
+            return
+        fixturemanager = metafunc.config.pluginmanager.get_plugin("funcmanage")
+        assert fixturemanager is not None
         # Add the scoped event loop fixture to Metafunc's list of fixture names and
         # fixturedefs and leave the actual parametrization to pytest
         # The fixture needs to be appended to avoid messing up the fixture evaluation

tests/async_fixtures/test_autouse_fixtures.py

@@ -0,0 +1,36 @@
+from textwrap import dedent
+
+from pytest import Pytester
+
+
+def test_autouse_fixture_in_different_scope_triggers_multiple_event_loop_error(
+    pytester: Pytester,
+):
+    pytester.makepyfile(
+        dedent(
+            """\
+            import asyncio
+            import pytest
+            import pytest_asyncio
+
+            loop: asyncio.AbstractEventLoop
+
+            @pytest_asyncio.fixture(autouse=True)
+            async def autouse_fixture():
+                pass
+
+            @pytest_asyncio.fixture(scope="session")
+            async def any_fixture():
+                global loop
+                loop = asyncio.get_running_loop()
+
+            @pytest.mark.asyncio(scope="session")
+            async def test_runs_in_session_scoped_loop(any_fixture):
+                global loop
+                assert asyncio.get_running_loop() is loop
+            """
+        )
+    )
+    result = pytester.runpytest("--asyncio-mode=strict")
+    result.assert_outcomes(errors=1)
+    result.stdout.fnmatch_lines("*MultipleEventLoopsRequestedError: *")