use assert[Not]IsInstance where appropriate
diff --git a/Lib/test/test_wsgiref.py b/Lib/test/test_wsgiref.py
index a3bc99f..a21d6e2 100755
--- a/Lib/test/test_wsgiref.py
+++ b/Lib/test/test_wsgiref.py
@@ -179,10 +179,10 @@
         # Check defaulting when empty
         env = {}
         util.setup_testing_defaults(env)
-        if isinstance(value,StringIO):
-            self.assertTrue(isinstance(env[key],StringIO))
+        if isinstance(value, StringIO):
+            self.assertIsInstance(env[key], StringIO)
         else:
-            self.assertEqual(env[key],value)
+            self.assertEqual(env[key], value)
 
         # Check existing value
         env = {key:alt}