'Adding a L{None}, representing C{*}, or a sequence that
includes L{None} to a L{MessageSet} whose
L{last<MessageSet.last>} property has been set replaces all
occurrences of L{None} with the value of
L{last<MessageSet.last>}.'

def test_lastOverridesNoneInAdd(self):

    hasLast = MessageSet(1)
    hasLast.last = 4
    hasLast.add(None)
    self.assertEqual(list(hasLast), [1, 4])
    self.assertEqual(list((hasLast + (None, 5))), [1, 4, 5])
    hasLast.add(3, None)
    self.assertEqual(list(hasLast), [1, 3, 4])
