fix: Do not try to initialize async fixtures without explicit asyncio…

… mark in strict mode.

This fixes a bug that breaks compatibility with pytest_trio.

Closes pytest-dev#298

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

CHANGELOG.rst

@@ -5,6 +5,7 @@ Changelog
 UNRELEASED
 =================
 - Adds `pytest-trio <https://pypi.org/project/pytest-trio/>`_ to the test dependencies
+- Fixes a bug that caused pytest-asyncio to try to set up async pytest_trio fixtures in strict mode. `#298 <https://github.com/pytest-dev/pytest-asyncio/issues/298>`_
 
 0.18.2 (22-03-03)
 =================

pytest_asyncio/plugin.py

@@ -210,7 +210,11 @@ def _preprocess_async_fixtures(config: Config, holder: Set[FixtureDef]) -> None:
                 # Nothing to do with a regular fixture function
                 continue
             if not _has_explicit_asyncio_mark(func):
-                if asyncio_mode == Mode.AUTO:
+                if asyncio_mode == Mode.STRICT:
+                    # Ignore async fixtures without explicit asyncio mark in strict mode
+                    # This applies to pytest_trio fixtures, for example
+                    continue
+                elif asyncio_mode == Mode.AUTO:
                     # Enforce asyncio mode if 'auto'
                     _set_explicit_asyncio_mark(func)
                 elif asyncio_mode == Mode.LEGACY:

tests/trio/test_fixtures.py

@@ -0,0 +1,25 @@
+from textwrap import dedent
+
+
+def test_strict_mode_ignores_trio_fixtures(testdir):
+    testdir.makepyfile(
+        dedent(
+            """\
+        import pytest
+        import pytest_asyncio
+        import pytest_trio
+
+        pytest_plugins = ["pytest_asyncio", "pytest_trio"]
+
+        @pytest_trio.trio_fixture
+        async def any_fixture():
+            return True
+
+        @pytest.mark.trio
+        async def test_anything(any_fixture):
+            pass
+        """
+        )
+    )
+    result = testdir.runpytest("--asyncio-mode=strict")
+    result.assert_outcomes(passed=1)