use assert[Not]IsInstance where appropriate
diff --git a/Lib/test/test_ntpath.py b/Lib/test/test_ntpath.py
index 83d794d..02dc38c 100644
--- a/Lib/test/test_ntpath.py
+++ b/Lib/test/test_ntpath.py
@@ -125,8 +125,8 @@
 
         # Issue 5827: Make sure normpath preserves unicode
         for path in (u'', u'.', u'/', u'\\', u'///foo/.//bar//'):
-            self.assertTrue(isinstance(ntpath.normpath(path), unicode),
-                            'normpath() returned str instead of unicode')
+            self.assertIsInstance(ntpath.normpath(path), unicode,
+                                  'normpath() returned str instead of unicode')
 
     def test_expandvars(self):
         with test_support.EnvironmentVarGuard() as env: