public void AddYearsTest() { var currentYear = new YearRange(TimeCalendar.New(April)); currentYear.AddYears(0).Should().Be(currentYear); var pastYear = currentYear.AddYears(-10); pastYear.Start.Should().Be(currentYear.Start.AddYears(-10)); pastYear.End.Should().Be(currentYear.End.AddYears(-10)); var futureYear = currentYear.AddYears(10); futureYear.Start.Should().Be(currentYear.Start.AddYears(10)); futureYear.End.Should().Be(currentYear.End.AddYears(10)); }