'If C{assertRaises} is used to create a context manager and no exception
is raised from the body of the C{with} statement then the C{with}
statement raises C{failureException} describing the lack of exception.'

def test_assertRaisesContextNoException(self):

    try:
        with self.assertRaises(ValueError):
            pass
    except self.failureException as exception:
        message = str(exception)
        self.assertEqual(message, 'ValueError    not    raised    (None    returned)')
    else:
        self.fail('Non-exception    result    should    have    caused    test    failure.')
