public void PreviousTest()
{
var my = new MonthYear(1, 2000);
var actual = my.Previous();
var expected = new MonthYear(12, 1999);
Assert.AreEqual(expected.Month, actual.Month);
Assert.AreEqual(expected.Year, actual.Year);
my = new MonthYear(2, 2000);
actual = my.Previous();
expected = new MonthYear(1, 2000);
Assert.AreEqual(expected.Month, actual.Month);
Assert.AreEqual(expected.Year, actual.Year);
}