System.Globalization.GregorianCalendar.GetDaysInMonth C# (CSharp) Method

        public override int GetDaysInMonth(int year, int month, int era) {
            if (era == CurrentEra || era == ADEra) {
                if (year < 1 || year > MaxYear) {
                    throw new ArgumentOutOfRangeException("year", String.Format(CultureInfo.CurrentCulture, Environment.GetResourceString("ArgumentOutOfRange_Range"),
                        1, MaxYear));
                }
                if (month < 1 || month > 12) {
                    throw new ArgumentOutOfRangeException("month", Environment.GetResourceString("ArgumentOutOfRange_Month"));
                }
                int[] days = ((year % 4 == 0 && (year % 100 != 0 || year % 400 == 0)) ? DaysToMonth366: DaysToMonth365);
                return (days[month] - days[month - 1]);
            }
            throw new ArgumentOutOfRangeException("era", Environment.GetResourceString("ArgumentOutOfRange_InvalidEraValue"));
        }

        public void GetDaysInMonthShouldReturnCorrectCount()
        {
            var target = new GregorianFiscalCalendar( 7 );
            var calendar = new GregorianCalendar();

            Assert.Equal( calendar.GetDaysInMonth( 2010, 7 ), target.GetDaysInMonth( 2011, 1 ) );
            Assert.Equal( calendar.GetDaysInMonth( 2010, 8 ), target.GetDaysInMonth( 2011, 2 ) );
            Assert.Equal( calendar.GetDaysInMonth( 2010, 6 ), target.GetDaysInMonth( 2010, 12 ) );
            Assert.Equal( calendar.GetDaysInMonth( 2011, 6 ), target.GetDaysInMonth( 2011, 12 ) );
        }