[fix] Fixes a bug that caused tests to run in the wrong event loop when requesting larger-scoped fixtures in a narrower-scoped test.

Previously, pytest-asyncio relied on marks applied to pytest Collectors (e.g. classes and modules) to determine the loop scope. This logic is no longer applicable for fixtures, because pytest-asyncio now relies on the asyncio mark applied to tests. As a result, fixtures were looking for an "asyncio" mark on surrounding collectors to no avail and defaulted to choosing a function-scoped loop.

This patch chooses the loop scope based on the fixture scope.

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

Author: seifertm

docs/source/reference/markers/class_scoped_loop_with_fixture_strict_mode_example.py

@@ -9,7 +9,7 @@
 class TestClassScopedLoop:
     loop: asyncio.AbstractEventLoop
 
-    @pytest_asyncio.fixture
+    @pytest_asyncio.fixture(scope="class")
     async def my_fixture(self):
         TestClassScopedLoop.loop = asyncio.get_running_loop()
 

pytest_asyncio/plugin.py

@@ -204,13 +204,6 @@ def _preprocess_async_fixtures(
     config = collector.config
     asyncio_mode = _get_asyncio_mode(config)
     fixturemanager = config.pluginmanager.get_plugin("funcmanage")
-    marker = collector.get_closest_marker("asyncio")
-    scope = marker.kwargs.get("scope", "function") if marker else "function"
-    if scope == "function":
-        event_loop_fixture_id = "event_loop"
-    else:
-        event_loop_node = _retrieve_scope_root(collector, scope)
-        event_loop_fixture_id = event_loop_node.stash.get(_event_loop_fixture_id, None)
     for fixtures in fixturemanager._arg2fixturedefs.values():
         for fixturedef in fixtures:
             func = fixturedef.func
@@ -222,6 +215,14 @@ def _preprocess_async_fixtures(
                 # Ignore async fixtures without explicit asyncio mark in strict mode
                 # This applies to pytest_trio fixtures, for example
                 continue
+            scope = fixturedef.scope
+            if scope == "function":
+                event_loop_fixture_id = "event_loop"
+            else:
+                event_loop_node = _retrieve_scope_root(collector, scope)
+                event_loop_fixture_id = event_loop_node.stash.get(
+                    _event_loop_fixture_id, None
+                )
             _make_asyncio_fixture_function(func)
             function_signature = inspect.signature(func)
             if "event_loop" in function_signature.parameters:
@@ -589,6 +590,12 @@ def scoped_event_loop(
         yield loop
         loop.close()
         asyncio.set_event_loop_policy(old_loop_policy)
+        # When a test uses both a scoped event loop and the event_loop fixture,
+        # the "_provide_clean_event_loop" finalizer of the event_loop fixture
+        # will already have installed a fresh event loop, in order to shield
+        # subsequent tests from side-effects. We close this loop before restoring
+        # the old loop to avoid ResourceWarnings.
+        asyncio.get_event_loop().close()
         asyncio.set_event_loop(old_loop)
 
     # @pytest.fixture does not register the fixture anywhere, so pytest doesn't
@@ -680,7 +687,9 @@ def pytest_generate_tests(metafunc: Metafunc) -> None:
             )
         # Add the scoped event loop fixture to Metafunc's list of fixture names and
         # fixturedefs and leave the actual parametrization to pytest
-        metafunc.fixturenames.insert(0, event_loop_fixture_id)
+        # The fixture needs to be appended to avoid messing up the fixture evaluation
+        # order
+        metafunc.fixturenames.append(event_loop_fixture_id)
         metafunc._arg2fixturedefs[
             event_loop_fixture_id
         ] = fixturemanager._arg2fixturedefs[event_loop_fixture_id]
@@ -885,8 +894,13 @@ def pytest_runtest_setup(item: pytest.Item) -> None:
     fixturenames = item.fixturenames  # type: ignore[attr-defined]
     # inject an event loop fixture for all async tests
     if "event_loop" in fixturenames:
+        # Move the "event_loop" fixture to the beginning of the fixture evaluation
+        # closure for backwards compatibility
         fixturenames.remove("event_loop")
-    fixturenames.insert(0, event_loop_fixture_id)
+        fixturenames.insert(0, "event_loop")
+    else:
+        if event_loop_fixture_id not in fixturenames:
+            fixturenames.append(event_loop_fixture_id)
     obj = getattr(item, "obj", None)
     if not getattr(obj, "hypothesis", False) and getattr(
         obj, "is_hypothesis_test", False
@@ -944,6 +958,12 @@ def _session_event_loop(
     yield loop
     loop.close()
     asyncio.set_event_loop_policy(old_loop_policy)
+    # When a test uses both a scoped event loop and the event_loop fixture,
+    # the "_provide_clean_event_loop" finalizer of the event_loop fixture
+    # will already have installed a fresh event loop, in order to shield
+    # subsequent tests from side-effects. We close this loop before restoring
+    # the old loop to avoid ResourceWarnings.
+    asyncio.get_event_loop().close()
     asyncio.set_event_loop(old_loop)
 
 

tests/async_fixtures/test_async_fixtures_with_finalizer.py

@@ -4,13 +4,13 @@
 import pytest
 
 
-@pytest.mark.asyncio
+@pytest.mark.asyncio(scope="module")
 async def test_module_with_event_loop_finalizer(port_with_event_loop_finalizer):
     await asyncio.sleep(0.01)
     assert port_with_event_loop_finalizer
 
 
-@pytest.mark.asyncio
+@pytest.mark.asyncio(scope="module")
 async def test_module_with_get_event_loop_finalizer(port_with_get_event_loop_finalizer):
     await asyncio.sleep(0.01)
     assert port_with_get_event_loop_finalizer

tests/markers/test_class_scope.py

@@ -220,3 +220,34 @@ async def test_runs_is_same_loop_as_fixture(self, my_fixture):
     )
     result = pytester.runpytest_subprocess("--asyncio-mode=strict")
     result.assert_outcomes(passed=1)
+
+
+def test_asyncio_mark_allows_combining_class_scoped_fixture_with_function_scoped_test(
+    pytester: pytest.Pytester,
+):
+    pytester.makepyfile(
+        dedent(
+            """\
+            import asyncio
+
+            import pytest
+            import pytest_asyncio
+
+            loop: asyncio.AbstractEventLoop
+
+            class TestMixedScopes:
+                @pytest_asyncio.fixture(scope="class")
+                async def async_fixture(self):
+                    global loop
+                    loop = asyncio.get_running_loop()
+
+                @pytest.mark.asyncio(scope="function")
+                async def test_runs_in_different_loop_as_fixture(self, async_fixture):
+                    global loop
+                    assert asyncio.get_running_loop() is not loop
+
+            """
+        ),
+    )
+    result = pytester.runpytest("--asyncio-mode=strict")
+    result.assert_outcomes(passed=1)

tests/markers/test_module_scope.py

@@ -219,3 +219,64 @@ async def test_runs_is_same_loop_as_fixture(my_fixture):
     )
     result = pytester.runpytest_subprocess("--asyncio-mode=strict")
     result.assert_outcomes(passed=1)
+
+
+def test_asyncio_mark_allows_combining_module_scoped_fixture_with_class_scoped_test(
+    pytester: Pytester,
+):
+    pytester.makepyfile(
+        dedent(
+            """\
+            import asyncio
+
+            import pytest
+            import pytest_asyncio
+
+            loop: asyncio.AbstractEventLoop
+
+            @pytest_asyncio.fixture(scope="module")
+            async def async_fixture():
+                global loop
+                loop = asyncio.get_running_loop()
+
+            @pytest.mark.asyncio(scope="class")
+            class TestMixedScopes:
+                async def test_runs_in_different_loop_as_fixture(self, async_fixture):
+                    global loop
+                    assert asyncio.get_running_loop() is not loop
+
+            """
+        ),
+    )
+    result = pytester.runpytest("--asyncio-mode=strict")
+    result.assert_outcomes(passed=1)
+
+
+def test_asyncio_mark_allows_combining_module_scoped_fixture_with_function_scoped_test(
+    pytester: Pytester,
+):
+    pytester.makepyfile(
+        __init__="",
+        test_mixed_scopes=dedent(
+            """\
+            import asyncio
+
+            import pytest
+            import pytest_asyncio
+
+            loop: asyncio.AbstractEventLoop
+
+            @pytest_asyncio.fixture(scope="module")
+            async def async_fixture():
+                global loop
+                loop = asyncio.get_running_loop()
+
+            @pytest.mark.asyncio(scope="function")
+            async def test_runs_in_different_loop_as_fixture(async_fixture):
+                global loop
+                assert asyncio.get_running_loop() is not loop
+            """
+        ),
+    )
+    result = pytester.runpytest("--asyncio-mode=strict")
+    result.assert_outcomes(passed=1)

tests/markers/test_package_scope.py

@@ -223,3 +223,94 @@ async def test_runs_in_same_loop_as_fixture(my_fixture):
     )
     result = pytester.runpytest_subprocess("--asyncio-mode=strict")
     result.assert_outcomes(passed=1)
+
+
+def test_asyncio_mark_allows_combining_package_scoped_fixture_with_module_scoped_test(
+    pytester: Pytester,
+):
+    pytester.makepyfile(
+        __init__="",
+        test_mixed_scopes=dedent(
+            """\
+            import asyncio
+
+            import pytest
+            import pytest_asyncio
+
+            loop: asyncio.AbstractEventLoop
+
+            @pytest_asyncio.fixture(scope="package")
+            async def async_fixture():
+                global loop
+                loop = asyncio.get_running_loop()
+
+            @pytest.mark.asyncio(scope="module")
+            async def test_runs_in_different_loop_as_fixture(async_fixture):
+                global loop
+                assert asyncio.get_running_loop() is not loop
+            """
+        ),
+    )
+    result = pytester.runpytest("--asyncio-mode=strict")
+    result.assert_outcomes(passed=1)
+
+
+def test_asyncio_mark_allows_combining_package_scoped_fixture_with_class_scoped_test(
+    pytester: Pytester,
+):
+    pytester.makepyfile(
+        __init__="",
+        test_mixed_scopes=dedent(
+            """\
+            import asyncio
+
+            import pytest
+            import pytest_asyncio
+
+            loop: asyncio.AbstractEventLoop
+
+            @pytest_asyncio.fixture(scope="package")
+            async def async_fixture():
+                global loop
+                loop = asyncio.get_running_loop()
+
+            @pytest.mark.asyncio(scope="class")
+            class TestMixedScopes:
+                async def test_runs_in_different_loop_as_fixture(self, async_fixture):
+                    global loop
+                    assert asyncio.get_running_loop() is not loop
+            """
+        ),
+    )
+    result = pytester.runpytest("--asyncio-mode=strict")
+    result.assert_outcomes(passed=1)
+
+
+def test_asyncio_mark_allows_combining_package_scoped_fixture_with_function_scoped_test(
+    pytester: Pytester,
+):
+    pytester.makepyfile(
+        __init__="",
+        test_mixed_scopes=dedent(
+            """\
+            import asyncio
+
+            import pytest
+            import pytest_asyncio
+
+            loop: asyncio.AbstractEventLoop
+
+            @pytest_asyncio.fixture(scope="package")
+            async def async_fixture():
+                global loop
+                loop = asyncio.get_running_loop()
+
+            @pytest.mark.asyncio
+            async def test_runs_in_different_loop_as_fixture(async_fixture):
+                global loop
+                assert asyncio.get_running_loop() is not loop
+            """
+        ),
+    )
+    result = pytester.runpytest("--asyncio-mode=strict")
+    result.assert_outcomes(passed=1)