bpo-41322: added deprecation warning for tests returning value!=None (GH-27748)

Author: akulakov

Lib/unittest/async_case.py

@@ -1,5 +1,6 @@
 import asyncio
 import inspect
+import warnings
 
 from .case import TestCase
 
@@ -62,7 +63,9 @@ def _callSetUp(self):
         self._callAsync(self.asyncSetUp)
 
     def _callTestMethod(self, method):
-        self._callMaybeAsync(method)
+        if self._callMaybeAsync(method) is not None:
+            warnings.warn(f'It is deprecated to return a value!=None from a '
+                          f'test case ({method})', DeprecationWarning)
 
     def _callTearDown(self):
         self._callAsync(self.asyncTearDown)

Lib/unittest/case.py

@@ -546,7 +546,9 @@ def _callSetUp(self):
         self.setUp()
 
     def _callTestMethod(self, method):
-        method()
+        if method() is not None:
+            warnings.warn(f'It is deprecated to return a value!=None from a '
+                          f'test case ({method})', DeprecationWarning)
 
     def _callTearDown(self):
         self.tearDown()

Misc/NEWS.d/next/Library/2021-08-12-16-22-16.bpo-41322.utscTd.rst

@@ -0,0 +1,3 @@
+Added ``DeprecationWarning`` for tests and async tests that return a
+value!=None (as this may indicate an improperly written test, for example a
+test written as a generator function).