public void NextTest()
        {
            var my = new MonthYear(1, 2000);
            var actual = my.Next();
            var expected = new MonthYear(2, 2000);
            Assert.AreEqual(expected.Month, actual.Month);
            Assert.AreEqual(expected.Year, actual.Year);

            my = new MonthYear(12, 2000);
            actual = my.Next();
            expected = new MonthYear(1, 2001);
            Assert.AreEqual(expected.Month, actual.Month);
            Assert.AreEqual(expected.Year, actual.Year);
        }