def test_arithmetic(self):
        utc_dt = self.transition_time

        for days in range(-420, 720, 20):
            delta = timedelta(days=days)

            # Make sure we can get back where we started
            dt = utc_dt.astimezone(self.tzinfo)
            dt2 = dt + delta
            dt2 = dt2 - delta
            self.assertEqual(dt, dt2)

            # Make sure arithmetic crossing DST boundaries ends
            # up in the correct timezone after normalization
            utc_plus_delta = (utc_dt + delta).astimezone(self.tzinfo)
            local_plus_delta = self.tzinfo.normalize(dt + delta)
            self.assertEqual(
                    prettydt(utc_plus_delta),
                    prettydt(local_plus_delta),
                    'Incorrect result for delta==%d days.  Wanted %r. Got %r'%(
                        days,
                        prettydt(utc_plus_delta),
                        prettydt(local_plus_delta),
                        )
                    )
dataset/ETHPy150Open awslabs/lambda-apigateway-twilio-tutorial/pytz/tests/test_tzinfo.py/USEasternDSTStartTestCase.test_arithmetic/original