System.Globalization.TaiwanCalendar.AddMonths C# (CSharp) Method

        public override DateTime AddMonths(DateTime time, int months) {
            return (helper.AddMonths(time, months));
        }

        private void VerificationHelper(DateTime value, int addValue)
        {
            System.Globalization.Calendar tc = new TaiwanCalendar();
            DateTime newDate = tc.AddMonths(value, addValue);
            int totalYear = addValue / 12;
            int leftMonth = addValue % 12;
            int day = value.Day;
            int month = value.Month + leftMonth;
            int year = value.Year + totalYear;
            if (month > 12)
            {
                month = month % 12;
                year++;
            }

            if (month < 1)
            {
                year--;
                month = 12 + month;
            }

            int dayInMonth = 0;
            if (IsLeapYear(year))
            {
                dayInMonth = _DAYS_PER_MONTHS_IN_LEAP_YEAR[month];
            }
            else
            {
                dayInMonth = _DAYS_PER_MONTHS_IN_NO_LEAP_YEAR[month];
            }

            day = day > dayInMonth ? dayInMonth : day;
            DateTime desiredDate = new DateTime(year, month, day, value.Hour, value.Minute, value.Second, value.Millisecond);

            Assert.Equal(desiredDate.Year, newDate.Year);
            Assert.Equal(desiredDate.Month, newDate.Month);
            Assert.Equal(desiredDate.Day, newDate.Day);
            Assert.Equal(desiredDate.Hour, newDate.Hour);
            Assert.Equal(desiredDate.Minute, newDate.Minute);
            Assert.Equal(desiredDate.Second, newDate.Second);
            Assert.Equal(desiredDate.Millisecond, newDate.Millisecond);
        }