use assert[Not]In where appropriate
diff --git a/Lib/test/test_tempfile.py b/Lib/test/test_tempfile.py
index d296fac..0076c48 100644
--- a/Lib/test/test_tempfile.py
+++ b/Lib/test/test_tempfile.py
@@ -113,7 +113,7 @@
         for i in range(TEST_FILES):
             s = next(r)
             self.nameCheck(s, '', '', '')
-            self.assertFalse(s in dict)
+            self.assertNotIn(s, dict)
             dict[s] = 1
 
     def supports_iter(self):