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

        public override bool IsLeapYear(int year, int era) {
            if (era == CurrentEra || era == ADEra) {
                if (year >= 1 && year <= MaxYear) {
                    return (year % 4 == 0 && (year % 100 != 0 || year % 400 == 0));
                }

                throw new ArgumentOutOfRangeException(
                            "year",
                            String.Format(
                                CultureInfo.CurrentCulture,
                                Environment.GetResourceString("ArgumentOutOfRange_Range"), 1, MaxYear));
            }
            throw new ArgumentOutOfRangeException("era", Environment.GetResourceString("ArgumentOutOfRange_InvalidEraValue"));
        }

        public void NpgsqlDateConstructors()
        {
            NpgsqlDate date;
            DateTime   dateTime;

            System.Globalization.Calendar calendar = new System.Globalization.GregorianCalendar();

            date = new NpgsqlDate();
            Assert.AreEqual(1, date.Day);
            Assert.AreEqual(DayOfWeek.Monday, date.DayOfWeek);
            Assert.AreEqual(1, date.DayOfYear);
            Assert.AreEqual(false, date.IsLeapYear);
            Assert.AreEqual(1, date.Month);
            Assert.AreEqual(1, date.Year);

            dateTime = new DateTime(2009, 5, 31);
            date     = new NpgsqlDate(dateTime);
            Assert.AreEqual(dateTime.Day, date.Day);
            Assert.AreEqual(dateTime.DayOfWeek, date.DayOfWeek);
            Assert.AreEqual(dateTime.DayOfYear, date.DayOfYear);
            Assert.AreEqual(calendar.IsLeapYear(2009), date.IsLeapYear);
            Assert.AreEqual(dateTime.Month, date.Month);
            Assert.AreEqual(dateTime.Year, date.Year);

            //Console.WriteLine(new DateTime(2009, 5, 31).Ticks);
            //Console.WriteLine((new DateTime(2009, 5, 31) - new DateTime(1, 1, 1)).TotalDays);
            // 2009-5-31
            dateTime = new DateTime(633793248000000000); // ticks since 1 Jan 1
            date     = new NpgsqlDate(733557);           // days since 1 Jan 1
            Assert.AreEqual(dateTime.Day, date.Day);
            Assert.AreEqual(dateTime.DayOfWeek, date.DayOfWeek);
            Assert.AreEqual(dateTime.DayOfYear, date.DayOfYear);
            Assert.AreEqual(calendar.IsLeapYear(2009), date.IsLeapYear);
            Assert.AreEqual(dateTime.Month, date.Month);
            Assert.AreEqual(dateTime.Year, date.Year);

            // copy previous value.  should get same result
            date = new NpgsqlDate(date);
            Assert.AreEqual(dateTime.Day, date.Day);
            Assert.AreEqual(dateTime.DayOfWeek, date.DayOfWeek);
            Assert.AreEqual(dateTime.DayOfYear, date.DayOfYear);
            Assert.AreEqual(calendar.IsLeapYear(2009), date.IsLeapYear);
            Assert.AreEqual(dateTime.Month, date.Month);
            Assert.AreEqual(dateTime.Year, date.Year);

#if NET6_0_OR_GREATER
            date = new NpgsqlDate(new DateOnly(2012, 3, 4));
            Assert.That(date.Year, Is.EqualTo(2012));
            Assert.That(date.Month, Is.EqualTo(3));
            Assert.That(date.Day, Is.EqualTo(4));
#endif
        }