fixtures: turn requesting async fixture without a plugin into a hard error

Deprecated feature scheduled for removal in pytest 9. Part of #13893.

Author: bluetech

doc/en/deprecations.rst

@@ -148,76 +148,6 @@ Simply remove the ``__init__.py`` file entirely.
 Python 3.3+ natively supports namespace packages without ``__init__.py``.
 
 
-.. _sync-test-async-fixture:
-
-sync test depending on async fixture
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-.. deprecated:: 8.4
-
-Pytest has for a long time given an error when encountering an asynchronous test function, prompting the user to install
-a plugin that can handle it. It has not given any errors if you have an asynchronous fixture that's depended on by a
-synchronous test. If the fixture was an async function you did get an "unawaited coroutine" warning, but for async yield fixtures you didn't even get that.
-This is a problem even if you do have a plugin installed for handling async tests, as they may require
-special decorators for async fixtures to be handled, and some may not robustly handle if a user accidentally requests an
-async fixture from their sync tests. Fixture values being cached can make this even more unintuitive, where everything will
-"work" if the fixture is first requested by an async test, and then requested by a synchronous test.
-
-Unfortunately there is no 100% reliable method of identifying when a user has made a mistake, versus when they expect an
-unawaited object from their fixture that they will handle on their own. To suppress this warning
-when you in fact did intend to handle this you can wrap your async fixture in a synchronous fixture:
-
-.. code-block:: python
-
-    import asyncio
-    import pytest
-
-
-    @pytest.fixture
-    async def unawaited_fixture():
-        return 1
-
-
-    def test_foo(unawaited_fixture):
-        assert 1 == asyncio.run(unawaited_fixture)
-
-should be changed to
-
-
-.. code-block:: python
-
-    import asyncio
-    import pytest
-
-
-    @pytest.fixture
-    def unawaited_fixture():
-        async def inner_fixture():
-            return 1
-
-        return inner_fixture()
-
-
-    def test_foo(unawaited_fixture):
-        assert 1 == asyncio.run(unawaited_fixture)
-
-
-You can also make use of `pytest_fixture_setup` to handle the coroutine/asyncgen before pytest sees it - this is the way current async pytest plugins handle it.
-
-If a user has an async fixture with ``autouse=True`` in their ``conftest.py``, or in a file
-containing both synchronous tests and the fixture, they will receive this warning.
-Unless you're using a plugin that specifically handles async fixtures
-with synchronous tests, we strongly recommend against this practice.
-It can lead to unpredictable behavior (with larger scopes, it may appear to "work" if an async
-test is the first to request the fixture, due to value caching) and will generate
-unawaited-coroutine runtime warnings (but only for non-yield fixtures).
-Additionally, it creates ambiguity for other developers about whether the fixture is intended to perform
-setup for synchronous tests.
-
-The `anyio pytest plugin <https://anyio.readthedocs.io/en/stable/testing.html>`_ supports
-synchronous tests with async fixtures, though certain limitations apply.
-
-
 .. _import-or-skip-import-error:
 
 ``pytest.importorskip`` default behavior regarding :class:`ImportError`
@@ -423,6 +353,78 @@ an appropriate period of deprecation has passed.
 
 Some breaking changes which could not be deprecated are also listed.
 
+.. _sync-test-async-fixture:
+
+sync test depending on async fixture
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. deprecated:: 8.4
+.. versionremoved:: 9.0
+
+Pytest has for a long time given an error when encountering an asynchronous test function, prompting the user to install
+a plugin that can handle it. It has not given any errors if you have an asynchronous fixture that's depended on by a
+synchronous test. If the fixture was an async function you did get an "unawaited coroutine" warning, but for async yield fixtures you didn't even get that.
+This is a problem even if you do have a plugin installed for handling async tests, as they may require
+special decorators for async fixtures to be handled, and some may not robustly handle if a user accidentally requests an
+async fixture from their sync tests. Fixture values being cached can make this even more unintuitive, where everything will
+"work" if the fixture is first requested by an async test, and then requested by a synchronous test.
+
+Unfortunately there is no 100% reliable method of identifying when a user has made a mistake, versus when they expect an
+unawaited object from their fixture that they will handle on their own. To suppress this warning
+when you in fact did intend to handle this you can wrap your async fixture in a synchronous fixture:
+
+.. code-block:: python
+
+    import asyncio
+    import pytest
+
+
+    @pytest.fixture
+    async def unawaited_fixture():
+        return 1
+
+
+    def test_foo(unawaited_fixture):
+        assert 1 == asyncio.run(unawaited_fixture)
+
+should be changed to
+
+
+.. code-block:: python
+
+    import asyncio
+    import pytest
+
+
+    @pytest.fixture
+    def unawaited_fixture():
+        async def inner_fixture():
+            return 1
+
+        return inner_fixture()
+
+
+    def test_foo(unawaited_fixture):
+        assert 1 == asyncio.run(unawaited_fixture)
+
+
+You can also make use of `pytest_fixture_setup` to handle the coroutine/asyncgen before pytest sees it - this is the way current async pytest plugins handle it.
+
+If a user has an async fixture with ``autouse=True`` in their ``conftest.py``, or in a file
+containing both synchronous tests and the fixture, they will receive this warning.
+Unless you're using a plugin that specifically handles async fixtures
+with synchronous tests, we strongly recommend against this practice.
+It can lead to unpredictable behavior (with larger scopes, it may appear to "work" if an async
+test is the first to request the fixture, due to value caching) and will generate
+unawaited-coroutine runtime warnings (but only for non-yield fixtures).
+Additionally, it creates ambiguity for other developers about whether the fixture is intended to perform
+setup for synchronous tests.
+
+The `anyio pytest plugin <https://anyio.readthedocs.io/en/stable/testing.html>`_ supports
+synchronous tests with async fixtures, though certain limitations apply.
+
+
+
 Applying a mark to a fixture function
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

src/_pytest/fixtures.py

@@ -66,7 +66,6 @@
 from _pytest.scope import _ScopeName
 from _pytest.scope import HIGH_SCOPES
 from _pytest.scope import Scope
-from _pytest.warning_types import PytestRemovedIn9Warning
 from _pytest.warning_types import PytestWarning
 
 
@@ -1178,18 +1177,11 @@ def pytest_fixture_setup(
         fixturefunc
     ):
         auto_str = " with autouse=True" if fixturedef._autouse else ""
-
-        warnings.warn(
-            PytestRemovedIn9Warning(
-                f"{request.node.name!r} requested an async fixture "
-                f"{request.fixturename!r}{auto_str}, with no plugin or hook that "
-                "handled it. This is usually an error, as pytest does not natively "
-                "support it. "
-                "This will turn into an error in pytest 9.\n"
-                "See: https://docs.pytest.org/en/stable/deprecations.html#sync-test-depending-on-async-fixture"
-            ),
-            # no stacklevel will point at users code, so we just point here
-            stacklevel=1,
+        fail(
+            f"{request.node.name!r} requested an async fixture {request.fixturename!r}{auto_str}, "
+            "with no plugin or hook that handled it. This is an error, as pytest does not natively support it.\n"
+            "See: https://docs.pytest.org/en/stable/deprecations.html#sync-test-depending-on-async-fixture",
+            pytrace=False,
         )
 
     try:

testing/acceptance_test.py

@@ -1307,7 +1307,7 @@ def test_3():
     result.assert_outcomes(failed=3)
 
 
-def test_warning_on_sync_test_async_fixture(pytester: Pytester) -> None:
+def test_error_on_sync_test_async_fixture(pytester: Pytester) -> None:
     pytester.makepyfile(
         test_sync="""
             import pytest
@@ -1324,23 +1324,17 @@ def test_foo(async_fixture):
                     pass
         """
     )
-    result = pytester.runpytest("-Wdefault::pytest.PytestRemovedIn9Warning")
+    result = pytester.runpytest()
+    result.assert_outcomes(errors=1)
     result.stdout.fnmatch_lines(
         [
-            "*== warnings summary ==*",
-            (
-                "*PytestRemovedIn9Warning: 'test_foo' requested an async "
-                "fixture 'async_fixture', with no plugin or hook that handled it. "
-                "This is usually an error, as pytest does not natively support it. "
-                "This will turn into an error in pytest 9."
-            ),
-            "  See: https://docs.pytest.org/en/stable/deprecations.html#sync-test-depending-on-async-fixture",
+            "'test_foo' requested an async fixture 'async_fixture', with no plugin or hook that handled it. "
+            "This is an error, as pytest does not natively support it."
         ]
     )
-    result.assert_outcomes(passed=1, warnings=1)
 
 
-def test_warning_on_sync_test_async_fixture_gen(pytester: Pytester) -> None:
+def test_error_on_sync_test_async_fixture_gen(pytester: Pytester) -> None:
     pytester.makepyfile(
         test_sync="""
             import pytest
@@ -1354,23 +1348,17 @@ def test_foo(async_fixture):
                 ...
         """
     )
-    result = pytester.runpytest("-Wdefault::pytest.PytestRemovedIn9Warning")
+    result = pytester.runpytest()
+    result.assert_outcomes(errors=1)
     result.stdout.fnmatch_lines(
         [
-            "*== warnings summary ==*",
-            (
-                "*PytestRemovedIn9Warning: 'test_foo' requested an async "
-                "fixture 'async_fixture', with no plugin or hook that handled it. "
-                "This is usually an error, as pytest does not natively support it. "
-                "This will turn into an error in pytest 9."
-            ),
-            "  See: https://docs.pytest.org/en/stable/deprecations.html#sync-test-depending-on-async-fixture",
+            "'test_foo' requested an async fixture 'async_fixture', with no plugin or hook that handled it. "
+            "This is an error, as pytest does not natively support it."
         ]
     )
-    result.assert_outcomes(passed=1, warnings=1)
 
 
-def test_warning_on_sync_test_async_autouse_fixture(pytester: Pytester) -> None:
+def test_error_on_sync_test_async_autouse_fixture(pytester: Pytester) -> None:
     pytester.makepyfile(
         test_sync="""
             import pytest
@@ -1388,21 +1376,15 @@ def test_foo(async_fixture):
                     pass
         """
     )
-    result = pytester.runpytest("-Wdefault::pytest.PytestRemovedIn9Warning")
+    result = pytester.runpytest()
+    result.assert_outcomes(errors=1)
     result.stdout.fnmatch_lines(
         [
-            "*== warnings summary ==*",
-            (
-                "*PytestRemovedIn9Warning: 'test_foo' requested an async "
-                "fixture 'async_fixture' with autouse=True, with no plugin or hook "
-                "that handled it. "
-                "This is usually an error, as pytest does not natively support it. "
-                "This will turn into an error in pytest 9."
-            ),
-            "  See: https://docs.pytest.org/en/stable/deprecations.html#sync-test-depending-on-async-fixture",
+            "'test_foo' requested an async fixture 'async_fixture' with autouse=True, "
+            "with no plugin or hook that handled it. "
+            "This is an error, as pytest does not natively support it."
         ]
     )
-    result.assert_outcomes(passed=1, warnings=1)
 
 
 def test_pdb_can_be_rewritten(pytester: Pytester) -> None: