Set default asyncio fixture loop scope to function

changelog.d/924.changed.rst

@@ -0,0 +1 @@
+The default value of ``asyncio_default_fixture_loop_scope`` is now ``function``. The deprecated unset behavior and warning have been removed.

pytest_asyncio/plugin.py

@@ -137,7 +137,7 @@ def pytest_addoption(parser: Parser, pluginmanager: PytestPluginManager) -> None
         "asyncio_default_fixture_loop_scope",
         type="string",
         help="default scope of the asyncio event loop used to execute async fixtures",
-        default=None,
+        default="function",
     )
     parser.addini(
         "asyncio_default_test_loop_scope",
@@ -271,16 +271,6 @@ def _collect_hook_loop_factories(
     return factories
 
 
-_DEFAULT_FIXTURE_LOOP_SCOPE_UNSET = """\
-The configuration option "asyncio_default_fixture_loop_scope" is unset.
-The event loop scope for asynchronous fixtures will default to the "fixture" caching \
-scope. Future versions of pytest-asyncio will default the loop scope for asynchronous \
-fixtures to "function" scope. Set the default fixture loop scope explicitly in order \
-to avoid unexpected behavior in the future. Valid fixture loop scopes are: \
-"function", "class", "module", "package", "session"
-"""
-
-
 def _validate_scope(scope: str | None, option_name: str) -> None:
     if scope is None:
         return
@@ -295,8 +285,6 @@ def _validate_scope(scope: str | None, option_name: str) -> None:
 def pytest_configure(config: Config) -> None:
     default_fixture_loop_scope = config.getini("asyncio_default_fixture_loop_scope")
     _validate_scope(default_fixture_loop_scope, "asyncio_default_fixture_loop_scope")
-    if not default_fixture_loop_scope:
-        warnings.warn(PytestDeprecationWarning(_DEFAULT_FIXTURE_LOOP_SCOPE_UNSET))
 
     default_test_loop_scope = config.getini("asyncio_default_test_loop_scope")
     _validate_scope(default_test_loop_scope, "asyncio_default_test_loop_scope")
@@ -925,11 +913,7 @@ def pytest_fixture_setup(fixturedef: FixtureDef, request) -> object | None:
         if not _is_coroutine_or_asyncgen(fixturedef.func):
             return (yield)
     default_loop_scope = request.config.getini("asyncio_default_fixture_loop_scope")
-    loop_scope = (
-        getattr(fixturedef.func, "_loop_scope", None)
-        or default_loop_scope
-        or fixturedef.scope
-    )
+    loop_scope = getattr(fixturedef.func, "_loop_scope", None) or default_loop_scope
     runner_fixture_id = f"_{loop_scope}_scoped_runner"
     runner = request.getfixturevalue(runner_fixture_id)
     # Prevent the runner closing before the fixture's async teardown.

tests/test_fixture_loop_scopes.py

@@ -35,6 +35,39 @@ async def test_runs_in_same_loop_as_fixture(fixture):
     result.assert_outcomes(passed=1)
 
 
+def test_default_fixture_loop_scope_is_function_when_unset(pytester: Pytester):
+    pytester.makepyfile(dedent("""
+              import asyncio
+              import pytest
+              import pytest_asyncio
+
+              fixture_loops = []
+
+              @pytest_asyncio.fixture
+              async def fixture_loop():
+                  loop = asyncio.get_running_loop()
+                  fixture_loops.append(loop)
+                  return loop
+
+              @pytest.mark.asyncio
+              async def test_fixture_uses_function_loop_scope(fixture_loop):
+                  assert asyncio.get_running_loop() is fixture_loop
+
+              @pytest.mark.asyncio
+              async def test_fixture_uses_new_function_loop(fixture_loop):
+                  assert asyncio.get_running_loop() is fixture_loop
+                  assert fixture_loops[0] is not fixture_loops[1]
+              """))
+
+    result = pytester.runpytest_subprocess("--asyncio-mode=strict", "-W", "error")
+    result.assert_outcomes(passed=2)
+    result.stdout.fnmatch_lines(
+        [
+            "*asyncio_default_fixture_loop_scope=function*",
+        ]
+    )
+
+
 @pytest.mark.parametrize("default_loop_scope", ("function", "module", "session"))
 def test_default_loop_scope_config_option_changes_fixture_loop_scope(
     pytester: Pytester,