Factor out helper code from importlib.test.extension.test_path_hook.
diff --git a/Lib/importlib/test/util.py b/Lib/importlib/test/util.py
index f41a661..2698ef4 100644
--- a/Lib/importlib/test/util.py
+++ b/Lib/importlib/test/util.py
@@ -2,6 +2,7 @@
 import imp
 import os.path
 from test.support import unlink
+import unittest
 import sys
 
 
@@ -9,7 +10,7 @@
     """Class decorator that nullifies tests that require a case-insensitive
     file system."""
     if sys.platform not in ('win32', 'darwin', 'cygwin'):
-        return object()
+        return unittest.TestCase
     else:
         return class_