gh-48330: assert warning is emitted on unittest.TestResult with no addDuration (#103309)

Author: iritkatriel

Lib/test/test_unittest/test_case.py

@@ -304,7 +304,8 @@ def defaultTestResult(self):
             def test(self):
                 pass
 
-        Foo('test').run()
+        with self.assertWarns(RuntimeWarning):
+            Foo('test').run()
 
     def test_deprecation_of_return_val_from_test(self):
         # Issue 41322 - deprecate return of value that is not None from a test