use assert method

Lib/test/test_structseq.py

@@ -8,7 +8,7 @@ class StructSeqTest(unittest.TestCase):
 
     def test_tuple(self):
         t = time.gmtime()
-        assert isinstance(t, tuple)
+        self.assertIsInstance(t, tuple)
         astuple = tuple(t)
         self.assertEqual(len(t), len(astuple))
         self.assertEqual(t, astuple)