Patch to allow unit tests to test for exceptions through a 'with' 
statement. Resulting (failing) test would look like this:

  import unittest

  class T(unittest.TestCase):
     def runTest(self):
        with self.assertRaises(KeyError):
           raise ValueError

This saves having to put exception raising tests into a try/except 
block, which is cool. And by cool I mean totally sweet.