Add pytest.register_fixture

changelog/12376.feature.rst

@@ -0,0 +1,7 @@
+Added :func:`pytest.register_fixture()` to register fixtures using an imperative interface.
+
+This is an advanced function intended for use by plugins.
+
+Normally, fixtures should be registered declaratively using the :func:`@pytest.fixture <pytest.fixture>` decorator.
+Pytest looks for these fixture definitions during the collection phase and registers them automatically.
+For some plugin usecases the declarative interface can be cumbersome or unviable, in which case this imperative interface can be used.

doc/en/deprecations.rst

@@ -37,7 +37,7 @@ node-based matching instead of fragile string prefix matching.
 
     # Use instead
     fixture_manager.parsefactories(holder=plugin_obj, node=directory_node)
-    fixture_manager._register_fixture(name="fix", func=func, node=directory_node)
+    pytest.register_fixture(name="fix", func=func, node=directory_node)
 
 The equivalent of passing ``nodeid=None`` (global visibility) is ``node=session``.
 

src/_pytest/fixtures.py

@@ -2322,3 +2322,62 @@ def _showfixtures_main(config: Config, session: Session) -> None:
 def write_docstring(tw: TerminalWriter, doc: str, indent: str = "    ") -> None:
     for line in doc.split("\n"):
         tw.line(indent + line)
+
+
+def register_fixture(
+    *,
+    name: str,
+    func: _FixtureFunc[object],
+    node: nodes.Node,
+    scope: Scope | ScopeName | Callable[[str, Config], ScopeName] = "function",
+    params: Sequence[object] | None = None,
+    ids: tuple[object | None, ...] | Callable[[Any], object | None] | None = None,
+    autouse: bool = False,
+) -> None:
+    """Register a fixture imperatively.
+
+    This is an advanced function intended for use by plugins.
+
+    Normally, fixtures should be registered declaratively using the
+    :func:`@pytest.fixture <pytest.fixture>` decorator. Pytest looks for these
+    fixture definitions during the collection phase and registers them
+    automatically. For some plugin usecases the declarative interface can be
+    cumbersome or unviable, in which case the imperative interface can be used.
+
+    Fixture registration is expected to happen during the collection phase, and
+    this is the only sanctioned use. However, to allow for more creative uses,
+    this is not enforced. But do so at your own risk!
+
+    .. versionadded: 9.1
+
+    :param name:
+        The fixture's name.
+    :param func:
+        The fixture's implementation function.
+    :param node:
+        The visibility of the fixture.
+
+        Only items that are descendents of this node in the collection tree will
+        be able to request this fixture. You can think of this as the place
+        where you would put the `@pytest.fixture`.
+
+        For global visibility, pass the :class:`session <pytest.Session>` node,
+        which is the root of the collection tree.
+    :param scope:
+        The fixture's scope.
+    :param params:
+        The fixture's parametrization params.
+    :param ids:
+        The fixture's IDs.
+    :param autouse:
+        Whether this is an autouse fixture.
+    """
+    node.session._fixturemanager._register_fixture(
+        name=name,
+        func=func,
+        node=node,
+        scope=scope,
+        params=params,
+        ids=ids,
+        autouse=autouse,
+    )

src/_pytest/python.py

@@ -591,7 +591,7 @@ def xunit_setup_module_fixture(request) -> Generator[None]:
             if teardown_module is not None:
                 _call_with_optional_argument(teardown_module, module)
 
-        self.session._fixturemanager._register_fixture(
+        fixtures.register_fixture(
             # Use a unique name to speed up lookup.
             name=f"_xunit_setup_module_fixture_{self.obj.__name__}",
             func=xunit_setup_module_fixture,
@@ -627,7 +627,7 @@ def xunit_setup_function_fixture(request) -> Generator[None]:
             if teardown_function is not None:
                 _call_with_optional_argument(teardown_function, function)
 
-        self.session._fixturemanager._register_fixture(
+        fixtures.register_fixture(
             # Use a unique name to speed up lookup.
             name=f"_xunit_setup_function_fixture_{self.obj.__name__}",
             func=xunit_setup_function_fixture,
@@ -807,7 +807,7 @@ def xunit_setup_class_fixture(request) -> Generator[None]:
                 func = getimfunc(teardown_class)
                 _call_with_optional_argument(func, cls)
 
-        self.session._fixturemanager._register_fixture(
+        fixtures.register_fixture(
             # Use a unique name to speed up lookup.
             name=f"_xunit_setup_class_fixture_{self.obj.__qualname__}",
             func=xunit_setup_class_fixture,
@@ -841,7 +841,7 @@ def xunit_setup_method_fixture(request) -> Generator[None]:
                 func = getattr(instance, teardown_name)
                 _call_with_optional_argument(func, method)
 
-        self.session._fixturemanager._register_fixture(
+        fixtures.register_fixture(
             # Use a unique name to speed up lookup.
             name=f"_xunit_setup_method_fixture_{self.obj.__qualname__}",
             func=xunit_setup_method_fixture,

src/_pytest/unittest.py

@@ -17,6 +17,7 @@
 from typing import TYPE_CHECKING
 from unittest import TestCase
 
+from _pytest import fixtures
 import _pytest._code
 from _pytest._code import ExceptionInfo
 from _pytest.compat import assert_never
@@ -170,7 +171,7 @@ def unittest_setup_class_fixture(
                 cleanup()
                 process_teardown_exceptions()
 
-        self.session._fixturemanager._register_fixture(
+        fixtures.register_fixture(
             # Use a unique name to speed up lookup.
             name=f"_unittest_setUpClass_fixture_{cls.__qualname__}",
             func=unittest_setup_class_fixture,
@@ -187,7 +188,7 @@ def unittest_skip_fixture(request: FixtureRequest) -> None:
             reason = getattr(cls, "__unittest_skip_why__", "")
             raise skip.Exception(reason, _use_item_location=True)
 
-        self.session._fixturemanager._register_fixture(
+        fixtures.register_fixture(
             name=f"_unittest_skip_fixture_{cls.__qualname__}",
             func=unittest_skip_fixture,
             node=self,
@@ -216,7 +217,7 @@ def unittest_setup_method_fixture(
             if teardown is not None:
                 teardown(self, request.function)
 
-        self.session._fixturemanager._register_fixture(
+        fixtures.register_fixture(
             # Use a unique name to speed up lookup.
             name=f"_unittest_setup_method_fixture_{cls.__qualname__}",
             func=unittest_setup_method_fixture,

src/pytest/__init__.py

@@ -26,6 +26,7 @@
 from _pytest.fixtures import FixtureDef
 from _pytest.fixtures import FixtureLookupError
 from _pytest.fixtures import FixtureRequest
+from _pytest.fixtures import register_fixture
 from _pytest.fixtures import yield_fixture  # type: ignore[deprecated]
 from _pytest.freeze_support import freeze_includes
 from _pytest.legacypath import TempdirFactory
@@ -177,6 +178,7 @@
     "param",
     "raises",
     "register_assert_rewrite",
+    "register_fixture",
     "set_trace",
     "skip",
     "version_tuple",

testing/python/fixtures.py

@@ -1914,12 +1914,11 @@ def test_register_fixture_ordered_by_visibility(self, pytester: Pytester) -> Non
             @pytest.hookimpl(wrapper=True)
             def pytest_collection(session):
                 result = yield
-                fm = session._fixturemanager
                 item = session.items[0]
-                fm._register_fixture(name="fix", func=lambda: "session1", node=session)
-                fm._register_fixture(name="fix", func=lambda fix: f"item1-{fix}", node=item)
-                fm._register_fixture(name="fix", func=lambda fix: f"item2-{fix}", node=item)
-                fm._register_fixture(name="fix", func=lambda: "session2", node=session)
+                pytest.register_fixture(name="fix", func=lambda: "session1", node=session)
+                pytest.register_fixture(name="fix", func=lambda fix: f"item1-{fix}", node=item)
+                pytest.register_fixture(name="fix", func=lambda fix: f"item2-{fix}", node=item)
+                pytest.register_fixture(name="fix", func=lambda: "session2", node=session)
                 return result
             """
         )