Index: Lib/test/test_posix.py
===================================================================
--- Lib/test/test_posix.py	(revision 83969)
+++ Lib/test/test_posix.py	(working copy)
@@ -400,13 +400,7 @@
     def test_initgroups(self):
         # find missing group
 
-        groups = sorted(self.saved_groups)
-        for g1,g2 in zip(groups[:-1], groups[1:]):
-            g = g1 + 1
-            if g < g2:
-                break
-        else:
-            g = g2 + 1
+        g = max(self.saved_groups) + 1
         name = pwd.getpwuid(posix.getuid()).pw_name
         posix.initgroups(name, g)
         self.assertIn(g, posix.getgroups())