Improved user-facing messages

tests/pending_manager_test.py

 #!/usr/bin/env python
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Unit tests for pending_manager.py."""
 
 import logging
 import os
 import re
@@ skipping 147 matching lines @@
     commit_message = (
         "commit(u'foo%s\\n\\n"
         "Review URL: http://nowhere/%d', "
         "u'author@example.com')") % (author_and_reviewer, issue)
     seq.append(commit_message)
 
     return seq
 
   def testNoVerification(self):
     try:
-      # Need at least one verification.
       self._get_pc([], [])
-      self.fail()
-    except AssertionError:
+    except ValueError:
       pass
+    else:
+      self.fail(msg='A PendingManager must require at least one verifier.')
+
     try:
       # Cannot have the same verifier two times.
       self._get_pc(
           [fake.FakeVerifier(base.SUCCEEDED)],
           [fake.FakeVerifier(base.SUCCEEDED)])
-      self.fail()
     except AssertionError:
       pass
+    else:
+      self.fail(msg='A PendingManager should not accept the same verifier'
+                ' two times.')
 
   def _check_1(self, pc, result):
     issue = 31337
     # 'initial' won't be sent if the pre-patch verification fails, this is to
     # not add noise for ignored CLs.
     send_initial_packet = (result == base.SUCCEEDED or pc.verifiers)
     self.assertEqual(len(pc.queue.iterate()), 0)
     pc.look_for_new_pending_commit()
     self.assertEqual(len(pc.queue.iterate()), 1)
     commit = pc.queue.get(issue)
@@ skipping 529 matching lines @@
     self.context.checkout.check_calls(
         self._prepare_apply_commit(0, issue))
 
 
 if __name__ == '__main__':
   logging.basicConfig(
       level=[logging.ERROR, logging.WARNING, logging.INFO, logging.DEBUG][
         min(sys.argv.count('-v'), 3)],
       format='%(levelname)5s %(module)15s(%(lineno)3d): %(message)s')
   unittest.main()