Implement event loop factory hook

Author: tjkuson

changelog.d/1164.added.rst

@@ -0,0 +1,3 @@
+Added the ``pytest_asyncio_loop_factories`` hook to parametrize asyncio tests with custom event loop factories.
+
+The hook now returns a mapping of factory names to loop factories, and ``pytest.mark.asyncio(loop_factories=[...])`` can be used to select a subset of configured factories per test.

docs/how-to-guides/custom_loop_factory.rst

@@ -0,0 +1,26 @@
+================================================
+How to use custom event loop factories for tests
+================================================
+
+pytest-asyncio can run asynchronous tests with custom event loop factories by implementing ``pytest_asyncio_loop_factories`` in ``conftest.py``. The hook returns a mapping from factory names to loop factory callables:
+
+.. code-block:: python
+
+   import asyncio
+
+   import pytest
+
+
+   class CustomEventLoop(asyncio.SelectorEventLoop):
+       pass
+
+
+   def pytest_asyncio_loop_factories(config, item):
+       return {
+           "stdlib": asyncio.new_event_loop,
+           "custom": CustomEventLoop,
+       }
+
+See :doc:`run_test_with_specific_loop_factories` for running tests with only a subset of configured factories.
+
+See :doc:`../reference/hooks` and :doc:`../reference/markers/index` for the hook and marker reference.

docs/how-to-guides/index.rst

@@ -10,6 +10,8 @@ How-To Guides
   change_fixture_loop
   change_default_fixture_loop
   change_default_test_loop
+  custom_loop_factory
+  run_test_with_specific_loop_factories
   run_class_tests_in_same_loop
   run_module_tests_in_same_loop
   run_package_tests_in_same_loop

docs/how-to-guides/run_test_with_specific_loop_factories.rst

@@ -0,0 +1,14 @@
+=========================================================
+How to run a test with specific event loop factories only
+=========================================================
+
+To run a test with only a subset of configured factories, use the ``loop_factories`` argument of ``pytest.mark.asyncio``:
+
+.. code-block:: python
+
+   import pytest
+
+
+   @pytest.mark.asyncio(loop_factories=["custom"])
+   async def test_only_with_custom_event_loop():
+       pass

docs/how-to-guides/uvloop.rst

@@ -2,8 +2,31 @@
 How to test with uvloop
 =======================
 
-Redefining the *event_loop_policy* fixture will parametrize all async tests. The following example causes all async tests to run multiple times, once for each event loop in the fixture parameters:
-Replace the default event loop policy in your *conftest.py:*
+Define a ``pytest_asyncio_loop_factories`` hook in your *conftest.py* that maps factory names to loop factories:
+
+.. code-block:: python
+
+    import uvloop
+
+
+    def pytest_asyncio_loop_factories(config, item):
+        return {
+            "uvloop": uvloop.new_event_loop,
+        }
+
+.. seealso::
+
+   :doc:`custom_loop_factory`
+      More details on the ``pytest_asyncio_loop_factories`` hook, including per-test factory selection and multiple factory parametrization.
+
+Using the event_loop_policy fixture
+-----------------------------------
+
+.. note::
+
+   ``asyncio.AbstractEventLoopPolicy`` is deprecated as of Python 3.14 (removal planned for 3.16), and ``uvloop.EventLoopPolicy`` will be removed alongside it. Prefer the hook approach above.
+
+For older versions of Python and uvloop, you can override the *event_loop_policy* fixture in your *conftest.py:*
 
 .. code-block:: python
 

docs/reference/hooks.rst

@@ -0,0 +1,16 @@
+=====
+Hooks
+=====
+
+``pytest_asyncio_loop_factories``
+=================================
+
+This hook returns a mapping from factory name strings to event loop factory callables for the current test item.
+
+By default, each pytest-asyncio test is run once per configured factory. Tests managed by other async plugins are unaffected. Synchronous tests are not parametrized. The configured loop scope still determines how long each event loop instance is kept alive.
+
+Factories should be callables without required parameters and should return an ``asyncio.AbstractEventLoop`` instance. The effective hook result must be a non-empty mapping of non-empty string names to callables.
+
+When multiple ``pytest_asyncio_loop_factories`` implementations are present, pytest-asyncio uses the first non-``None`` result in pytest's hook dispatch order.
+
+When the hook is defined, async tests are parametrized via ``pytest.metafunc.parametrize``, and mapping keys are used as test IDs. For example, a test ``test_example`` with an event loop factory key ``foo`` will appear as ``test_example[foo]`` in test output.

docs/reference/index.rst

@@ -8,6 +8,7 @@ Reference
   configuration
   fixtures/index
   functions
+  hooks
   markers/index
   decorators/index
   changelog

docs/reference/markers/index.rst

@@ -36,6 +36,8 @@ Subpackages do not share the loop with their parent package.
 
 Tests marked with *session* scope share the same event loop, even if the tests exist in different packages.
 
+The ``pytest.mark.asyncio`` marker also accepts a ``loop_factories`` keyword argument to select a subset of configured event loop factories for a test. If ``loop_factories`` contains unknown names, pytest-asyncio raises a ``pytest.UsageError`` during collection.
+
 .. |auto mode| replace:: *auto mode*
 .. _auto mode: ../../concepts.html#auto-mode
 .. |pytestmark| replace:: ``pytestmark``