test_multipart_one_part(): Idempotency test case for a multipart/*

with only one subpart.

Lib/test/test_email.py

-# Copyright (C) 2001 Python Software Foundation
+# Copyright (C) 2001,2002 Python Software Foundation
 # email package unit tests
 
 import os
@@ -790,6 +790,10 @@ class TestIdempotent(unittest.TestCase):
         msg, text = self._msgobj('msg_21.txt')
         self._idempotent(msg, text)
 
+    def test_multipart_one_part(self):
+        msg, text = self._msgobj('msg_23.txt')
+        self._idempotent(msg, text)
+
     def test_content_type(self):
         eq = self.assertEquals
         # Get a message object and reset the seek pointer for other tests