use assert[Not]In where appropriate
diff --git a/Lib/test/test_warnings.py b/Lib/test/test_warnings.py
index d093994..e008984 100644
--- a/Lib/test/test_warnings.py
+++ b/Lib/test/test_warnings.py
@@ -472,7 +472,7 @@
             with test_support.captured_output('stderr') as stream:
                 self.module.warn(text)
                 result = stream.getvalue()
-        self.assertTrue(text in result)
+        self.assertIn(text, result)
 
     def test_showwarning_not_callable(self):
         with original_warnings.catch_warnings(module=self.module):