correct-class-fixtures (#10819) (#14011)

changelog/10819.bugfix.rst

@@ -0,0 +1,3 @@
+Fixed class-scoped fixtures defined in base classes not binding to the correct test instance when inherited by child test classes -- by :user:`yastcher`.
+
+Fixes :issue:`10819` and :issue:`14011`.

src/_pytest/fixtures.py

@@ -1148,6 +1148,10 @@ def resolve_fixture_function(
     # request.instance so that code working with "fixturedef" behaves
     # as expected.
     instance = request.instance
+
+    if instance is None and fixturedef._scope is Scope.Class:
+        instance = getattr(request._pyfuncitem, "instance", None)
+
     if instance is not None:
         # Handle the case where fixture is defined not in a test class, but some other class
         # (for example a plugin class with a fixture), see #2270.

testing/test_inherit_class_fixture.py

@@ -0,0 +1,70 @@
+from __future__ import annotations
+
+import typing
+
+import pytest
+
+
+class ParentBase:
+    """from issue #14011"""
+
+    name = ""
+    variable = ""
+
+    def setup(self) -> None:
+        self.variable = self.name
+
+    def teardown(self) -> None:
+        pass
+
+    @pytest.fixture(scope="class")
+    def fix(self) -> typing.Generator[None]:
+        self.setup()
+        yield
+        self.teardown()
+
+    @pytest.fixture(scope="class", autouse=True)
+    def base_autouse(self) -> None:
+        self.flag = True
+
+
+@pytest.mark.usefixtures("fix")
+class Test1(ParentBase):
+    name = "test1"
+
+    def test_a(self) -> None:
+        assert self.variable == self.name
+
+
+@pytest.mark.usefixtures("fix")
+class Test2(ParentBase):
+    name = "test2"
+
+    def test_a(self) -> None:
+        assert self.variable == self.name
+
+
+class TestChild(ParentBase):
+    def test_flag(self) -> None:
+        assert self.flag
+
+
+class BaseTestClass:
+    """from issue #10819"""
+
+    test_func_scope_set = None
+    test_class_scope_set = None
+
+    @pytest.fixture(scope="class", autouse=True)
+    def dummy_class_fixture(self) -> None:
+        self.test_class_scope_set = True
+
+    @pytest.fixture(scope="function", autouse=True)
+    def dummy_func_fixture(self) -> None:
+        self.test_func_scope_set = True
+
+
+class TestDummy(BaseTestClass):
+    def test_dummy(self) -> None:
+        assert self.test_func_scope_set is True
+        assert self.test_class_scope_set is True