Index: test_util.py
===================================================================
--- test_util.py	(revision 70302)
+++ test_util.py	(working copy)
@@ -51,7 +51,9 @@
         os.path.join = self.join
         os.path.isabs = self.isabs
         os.path.splitdrive = self.splitdrive
-        if self.uname is not None:
+        if self.uname is None:
+            del os.uname
+        else:
             os.uname = self.uname
 
     def _set_uname(self, uname):