@@ -41,7 +41,7 @@ def test_makefile_test_folders(self):
         idle_test = 'idlelib/idle_test'
         self.assertIn(idle_test, test_dirs)
 
-        used = [idle_test]
+        used = set([idle_test])
         for dirpath, dirs, files in os.walk(support.TEST_HOME_DIR):
             dirname = os.path.basename(dirpath)
             # Skip temporary dirs:
@@ -65,13 +65,14 @@ def test_makefile_test_folders(self):
                         "of test directories to install"
                     )
                 )
-                used.append(relpath)
+                used.add(relpath)
 
         # Don't check the wheel dir when Python is built --with-wheel-pkg-dir
         if sysconfig.get_config_var('WHEEL_PKG_DIR'):
             test_dirs.remove('test/wheeldata')
+            used.discard('test/wheeldata')
 
         # Check that there are no extra entries:
         unique_test_dirs = set(test_dirs)
-        self.assertSetEqual(unique_test_dirs, set(used))
+        self.assertSetEqual(unique_test_dirs, used)
         self.assertEqual(len(test_dirs), len(unique_test_dirs))