The test used int(time.time()) to get a random number, but this doesn't work on the mac (where times are bigger than ints). Changed to int(time.time()%1000000).
diff --git a/Lib/test/test_mailbox.py b/Lib/test/test_mailbox.py
index b9887ca..57a8316 100644
--- a/Lib/test/test_mailbox.py
+++ b/Lib/test/test_mailbox.py
@@ -39,7 +39,7 @@
         os.rmdir(self._dir)
 
     def createMessage(self, dir):
-        t = int(time.time())
+        t = int(time.time() % 1000000)
         pid = self._counter
         self._counter += 1
         filename = "%s.%s.myhostname.mydomain" % (t, pid)