'L{MessageSet.extend} accepts as its arugment an L{int} or
L{None}, or a sequence L{int}s or L{None}s of length two, or
another L{MessageSet}, combining its argument with its
instance\'s existing ranges.'

def test_extend(self):

    extendWithInt = MessageSet()
    extendWithInt.extend(1)
    self.assertEqual(list(extendWithInt), [1])
    extendWithNone = MessageSet()
    extendWithNone.extend(None)
    self.assertEqual(str(extendWithNone), '*')
    extendWithSequenceOfInts = MessageSet()
    extendWithSequenceOfInts.extend((1, 3))
    self.assertEqual(list(extendWithSequenceOfInts), [1, 2, 3])
    extendWithSequenceOfNones = MessageSet()
    extendWithSequenceOfNones.extend((None, None))
    self.assertEqual(str(extendWithSequenceOfNones), '*')
    extendWithMessageSet = MessageSet()
    extendWithMessageSet.extend(MessageSet(1, 3))
    self.assertEqual(list(extendWithMessageSet), [1, 2, 3])
