public void TestDecrease() { Assert.AreEqual(WeekDays.Tuesday, EnumHelper.DecreaseValue(WeekDays.Friday, 3)); Assert.AreEqual(WeekDays.Tuesday, EnumHelper.DecreaseValue(WeekDays.Tuesday, 0)); Assert.AreEqual(WeekDays.Monday, EnumHelper.DecreaseValue(WeekDays.Tuesday, 22)); try { EnumHelper.DecreaseValue(WeekDays.Tuesday, 22, true); Assert.Fail("Error expected"); } catch (Exception ex) { Assert.AreEqual(ex.Message, "The modifier 22 exceeds the minimum possible value for WeekDays when applied on Tuesday"); } }