def test_as_but_no_rate(self):
        tv = TimeValue(TimeOffset(4))
        with self.assertRaises(ValueError):
            tv.as_count()

        tv = TimeValue(100)
        with self.assertRaises(ValueError):
            tv.as_timeoffset()
    def test_as_timeoffset(self):
        tv = TimeValue(TimeOffset(4), rate=Fraction(25))
        to = tv.as_timeoffset()
        self.assertIsInstance(to, TimeOffset)
        self.assertEqual(to, TimeOffset(4))

        tv = TimeValue(Timestamp(4), rate=Fraction(25))
        to = tv.as_timeoffset()
        self.assertIsInstance(to, TimeOffset)
        self.assertEqual(to, TimeOffset(4))

        tv = TimeValue(100, rate=Fraction(25))
        to = tv.as_timeoffset()
        self.assertIsInstance(to, TimeOffset)
        self.assertEqual(to, TimeOffset(4))