Class tricky_notok

Lib/test/datetimetester.py:6011–6016

        # whether DST is assumed to be in effect.  In this situation,
        # a ValueError should be raised by astimezone().
        class tricky_notok(ok):
            def dst(self, dt):
                if dt.year == 2000:
                    return None
                else:
                    return 10*HOUR
        dt = self.theclass(2001, 1, 1).replace(tzinfo=utc_real)
        self.assertRaises(ValueError, dt.astimezone, tricky_notok())