use assert[Not]IsInstance where appropriate
diff --git a/Lib/test/test_future.py b/Lib/test/test_future.py
index 81d0a3e..84f9c47 100644
--- a/Lib/test/test_future.py
+++ b/Lib/test/test_future.py
@@ -109,7 +109,7 @@
     def test_unicode_literals_exec(self):
         scope = {}
         exec "from __future__ import unicode_literals; x = ''" in scope
-        self.assertTrue(isinstance(scope["x"], unicode))
+        self.assertIsInstance(scope["x"], unicode)
 
 
 def test_main():