diff --git a/Lib/test/test_mailbox.py b/Lib/test/test_mailbox.py
index d0538be..480d586 100644
--- a/Lib/test/test_mailbox.py
+++ b/Lib/test/test_mailbox.py
@@ -20,7 +20,7 @@
 # Silence Py3k warning
 rfc822 = test_support.import_module('rfc822', deprecated=True)
 
-class TestBase(unittest.TestCase):
+class TestBase:
 
     def _check_sample(self, msg):
         # Inspect a mailbox.Message representation of the sample message
@@ -429,7 +429,7 @@
         return self._path + '.lock'
 
 
-class TestMailboxSuperclass(TestBase):
+class TestMailboxSuperclass(TestBase, unittest.TestCase):
 
     def test_notimplemented(self):
         # Test that all Mailbox methods raise NotImplementedException.
@@ -464,7 +464,7 @@
         self.assertRaises(NotImplementedError, lambda: box.close())
 
 
-class TestMaildir(TestMailbox):
+class TestMaildir(TestMailbox, unittest.TestCase):
 
     _factory = lambda self, path, factory=None: mailbox.Maildir(path, factory)
 
@@ -914,7 +914,7 @@
         self._box.close()
 
 
-class TestMbox(_TestMboxMMDF):
+class TestMbox(_TestMboxMMDF, unittest.TestCase):
 
     _factory = lambda self, path, factory=None: mailbox.mbox(path, factory)
 
@@ -937,12 +937,12 @@
             perms = st.st_mode
             self.assertFalse((perms & 0111)) # Execute bits should all be off.
 
-class TestMMDF(_TestMboxMMDF):
+class TestMMDF(_TestMboxMMDF, unittest.TestCase):
 
     _factory = lambda self, path, factory=None: mailbox.MMDF(path, factory)
 
 
-class TestMH(TestMailbox):
+class TestMH(TestMailbox, unittest.TestCase):
 
     _factory = lambda self, path, factory=None: mailbox.MH(path, factory)
 
@@ -1074,7 +1074,7 @@
         return os.path.join(self._path, '.mh_sequences.lock')
 
 
-class TestBabyl(TestMailbox):
+class TestBabyl(TestMailbox, unittest.TestCase):
 
     _factory = lambda self, path, factory=None: mailbox.Babyl(path, factory)
 
@@ -1103,7 +1103,7 @@
         self.assertEqual(set(self._box.get_labels()), set(['blah']))
 
 
-class TestMessage(TestBase):
+class TestMessage(TestBase, unittest.TestCase):
 
     _factory = mailbox.Message      # Overridden by subclasses to reuse tests
 
@@ -1174,7 +1174,7 @@
         pass
 
 
-class TestMaildirMessage(TestMessage):
+class TestMaildirMessage(TestMessage, unittest.TestCase):
 
     _factory = mailbox.MaildirMessage
 
@@ -1249,7 +1249,7 @@
         self._check_sample(msg)
 
 
-class _TestMboxMMDFMessage(TestMessage):
+class _TestMboxMMDFMessage:
 
     _factory = mailbox._mboxMMDFMessage
 
@@ -1296,12 +1296,12 @@
                                  r"\d{2} \d{4}", msg.get_from()))
 
 
-class TestMboxMessage(_TestMboxMMDFMessage):
+class TestMboxMessage(_TestMboxMMDFMessage, TestMessage):
 
     _factory = mailbox.mboxMessage
 
 
-class TestMHMessage(TestMessage):
+class TestMHMessage(TestMessage, unittest.TestCase):
 
     _factory = mailbox.MHMessage
 
@@ -1332,7 +1332,7 @@
         self.assertEqual(msg.get_sequences(), ['foobar', 'replied'])
 
 
-class TestBabylMessage(TestMessage):
+class TestBabylMessage(TestMessage, unittest.TestCase):
 
     _factory = mailbox.BabylMessage
 
@@ -1387,12 +1387,12 @@
             self.assertEqual(visible[header], msg[header])
 
 
-class TestMMDFMessage(_TestMboxMMDFMessage):
+class TestMMDFMessage(_TestMboxMMDFMessage, TestMessage):
 
     _factory = mailbox.MMDFMessage
 
 
-class TestMessageConversion(TestBase):
+class TestMessageConversion(TestBase, unittest.TestCase):
 
     def test_plain_to_x(self):
         # Convert Message to all formats
@@ -1715,7 +1715,7 @@
         proxy.close()
 
 
-class TestProxyFile(TestProxyFileBase):
+class TestProxyFile(TestProxyFileBase, unittest.TestCase):
 
     def setUp(self):
         self._path = test_support.TESTFN
@@ -1764,7 +1764,7 @@
         self._test_close(mailbox._ProxyFile(self._file))
 
 
-class TestPartialFile(TestProxyFileBase):
+class TestPartialFile(TestProxyFileBase, unittest.TestCase):
 
     def setUp(self):
         self._path = test_support.TESTFN