warn if asyncio test requests async pytest fixture in strict mode

docs/reference/changelog.rst

@@ -2,6 +2,10 @@
 Changelog
 =========
 
+0.25.0 (UNRELEASED)
+===================
+- Deprecated: Added warning when asyncio test requests async ``@pytest.fixture`` in strict mode. This will become an error in a future version of flake8-asyncio. `#979 <https://github.com/pytest-dev/pytest-asyncio/pull/979>`_
+
 0.24.0 (2024-08-22)
 ===================
 - BREAKING: Updated minimum supported pytest version to v8.2.0

pytest_asyncio/plugin.py

@@ -880,7 +880,32 @@ def pytest_pyfunc_call(pyfuncitem: Function) -> object | None:
     """
     if pyfuncitem.get_closest_marker("asyncio") is not None:
         if isinstance(pyfuncitem, PytestAsyncioFunction):
-            pass
+            asyncio_mode = _get_asyncio_mode(pyfuncitem.config)
+            for fixname, fixtures in pyfuncitem._fixtureinfo.name2fixturedefs.items():
+                # name2fixturedefs is a dict between fixture name and a list of matching
+                # fixturedefs. The last entry in the list is closest and the one used.
+                func = fixtures[-1].func
+                if (
+                    _is_coroutine_or_asyncgen(func)
+                    and not _is_asyncio_fixture_function(func)
+                    and asyncio_mode == Mode.STRICT
+                ):
+                    warnings.warn(
+                        PytestDeprecationWarning(
+                            f"asyncio test {pyfuncitem.name!r} requested async "
+                            "@pytest.fixture "
+                            f"{fixname!r} in strict mode. "
+                            "You might want to use @pytest_asyncio.fixture or switch "
+                            "to auto mode. "
+                            "This will become an error in future versions of "
+                            "flake8-asyncio."
+                        ),
+                        stacklevel=1,
+                    )
+                    # no stacklevel points at the users code, so we set stacklevel=1
+                    # so it at least indicates that it's the plugin complaining.
+                    # Pytest gives the test file & name in the warnings summary at least
+
         else:
             pyfuncitem.warn(
                 pytest.PytestWarning(

tests/modes/test_strict_mode.py

@@ -124,3 +124,90 @@ async def test_anything(any_fixture):
             "*coroutine 'any_fixture' was never awaited*",
         ],
     )
+
+
+def test_strict_mode_marked_test_unmarked_fixture_warning(pytester: Pytester):
+    pytester.makeini("[pytest]\nasyncio_default_fixture_loop_scope = function")
+    pytester.makepyfile(
+        dedent(
+            """\
+        import pytest
+
+        # Not using pytest_asyncio.fixture
+        @pytest.fixture()
+        async def any_fixture():
+            pass
+
+        @pytest.mark.asyncio
+        async def test_anything(any_fixture):
+            # suppress unawaited coroutine warning
+            try:
+                any_fixture.send(None)
+            except StopIteration:
+                pass
+        """
+        )
+    )
+    result = pytester.runpytest_subprocess("--asyncio-mode=strict", "-W default")
+    result.assert_outcomes(passed=1, failed=0, skipped=0, warnings=1)
+    result.stdout.fnmatch_lines(
+        [
+            "*warnings summary*",
+            (
+                "test_strict_mode_marked_test_unmarked_fixture_warning.py::"
+                "test_anything"
+            ),
+            (
+                "*/pytest_asyncio/plugin.py:*: PytestDeprecationWarning: "
+                "asyncio test 'test_anything' requested async "
+                "@pytest.fixture 'any_fixture' in strict mode. "
+                "You might want to use @pytest_asyncio.fixture or switch to "
+                "auto mode. "
+                "This will become an error in future versions of flake8-asyncio."
+            ),
+        ],
+    )
+
+
+# autouse is not handled in any special way currently
+def test_strict_mode_marked_test_unmarked_autouse_fixture_warning(pytester: Pytester):
+    pytester.makeini("[pytest]\nasyncio_default_fixture_loop_scope = function")
+    pytester.makepyfile(
+        dedent(
+            """\
+        import pytest
+
+        # Not using pytest_asyncio.fixture
+        @pytest.fixture(autouse=True)
+        async def any_fixture():
+            pass
+
+        @pytest.mark.asyncio
+        async def test_anything(any_fixture):
+            # suppress unawaited coroutine warning
+            try:
+                any_fixture.send(None)
+            except StopIteration:
+                pass
+        """
+        )
+    )
+    result = pytester.runpytest_subprocess("--asyncio-mode=strict", "-W default")
+    result.assert_outcomes(passed=1, warnings=1)
+    result.stdout.fnmatch_lines(
+        [
+            "*warnings summary*",
+            (
+                "test_strict_mode_marked_test_unmarked_autouse_fixture_warning.py::"
+                "test_anything"
+            ),
+            (
+                "*/pytest_asyncio/plugin.py:*: PytestDeprecationWarning: "
+                "*asyncio test 'test_anything' requested async "
+                "@pytest.fixture 'any_fixture' in strict mode. "
+                "You might want to use @pytest_asyncio.fixture or switch to "
+                "auto mode. "
+                "This will become an error in future versions of flake8-asyncio."
+            ),
+        ],
+    )