Give warning when test function return other than None

AUTHORS

@@ -63,6 +63,7 @@ Ceridwen
 Charles Cloud
 Charles Machalow
 Charnjit SiNGH (CCSJ)
+Cheuk Ting Ho
 Chris Lamb
 Chris NeJame
 Chris Rose

changelog/7337.improvement.rst

@@ -0,0 +1 @@
+Warns for test functions that return non-None. Now in `pytest_pyfunc_call` after the `async_warn_and_skip` it will check for if the return is something other than None.

src/_pytest/python.py

@@ -77,10 +77,12 @@
 from _pytest.pathlib import visit
 from _pytest.scope import Scope
 from _pytest.warning_types import PytestCollectionWarning
+from _pytest.warning_types import PytestReturnNotNoneWarning
 from _pytest.warning_types import PytestUnhandledCoroutineWarning
 
 if TYPE_CHECKING:
     from typing_extensions import Literal
+
     from _pytest.scope import _ScopeName
 
 
@@ -192,6 +194,14 @@ def pytest_pyfunc_call(pyfuncitem: "Function") -> Optional[object]:
     result = testfunction(**testargs)
     if hasattr(result, "__await__") or hasattr(result, "__aiter__"):
         async_warn_and_skip(pyfuncitem.nodeid)
+    elif result is not None:
+        warnings.warn(
+            PytestReturnNotNoneWarning(
+                "Test function returning {result}, do you mean to use `assert` instead or `return`?".format(
+                    result=result
+                )
+            )
+        )
     return True
 
 

src/_pytest/warning_types.py

@@ -42,6 +42,13 @@ class PytestCollectionWarning(PytestWarning):
     __module__ = "pytest"
 
 
+@final
+class PytestReturnNotNoneWarning(PytestWarning):
+    """Warning emitted when a test function is returning value other than None."""
+
+    __module__ = "pytest"
+
+
 class PytestDeprecationWarning(PytestWarning, DeprecationWarning):
     """Warning class for features that will be removed in a future version."""
 

testing/acceptance_test.py

@@ -1292,3 +1292,14 @@ def test_no_brokenpipeerror_message(pytester: Pytester) -> None:
 
     # Cleanup.
     popen.stderr.close()
+
+
+def test_function_return_non_none_warning(testdir) -> None:
+    testdir.makepyfile(
+        """
+        def test_stuff():
+            return "something"
+    """
+    )
+    res = testdir.runpytest()
+    res.stdout.fnmatch_lines(["*PytestReturnNotNoneWarning: Test function returning*"])