feat: issue PytestCollectionWarning when tests used pytest.fixrure

Author: dongfangtianyu

changelog/12989.improvement.rst

@@ -0,0 +1 @@
+A warning is now issued when tests incorrectly use :class:`@pytest.fixture`, whereas this was previously silently ignored.

src/_pytest/python.py

@@ -354,6 +354,16 @@ def classnamefilter(self, name: str) -> bool:
 
     def istestfunction(self, obj: object, name: str) -> bool:
         if self.funcnamefilter(name) or self.isnosetest(obj):
+            if isinstance(obj, fixtures.FixtureFunctionDefinition):
+                self.warn(
+                    PytestCollectionWarning(
+                        f"cannot collect test function {name!r},"
+                        f"because it used the '@pytest.fixture' than becomes a fixture "
+                        f"(from: {self.nodeid})"
+                    )
+                )
+                return False
+
             if isinstance(obj, (staticmethod, classmethod)):
                 # staticmethods and classmethods need to be unwrapped.
                 obj = safe_getattr(obj, "__func__", False)

testing/python/collect.py

@@ -783,6 +783,26 @@ def test_function_with_square_brackets(self, pytester: Pytester) -> None:
             ]
         )
 
+    @pytest.mark.filterwarnings("default::UserWarning")
+    def test_function_used_fixture(self, pytester: Pytester):
+        pytester.makeini("[pytest]")
+        pytester.makepyfile(
+            """
+            import pytest
+            @pytest.fixture
+            def test_function():
+                pass
+        """
+        )
+        result = pytester.runpytest()
+        result.stdout.fnmatch_lines(
+            [
+                "collected 0 items",
+                "*== warnings summary ==*",
+                "*because it used the '@pytest.fixture' than becomes a fixture*",
+            ]
+        )
+
 
 class TestSorting:
     def test_check_equality(self, pytester: Pytester) -> None: