public void TestCheckIfIsSundayReturnsFalseOnANonSundayDate()
        {
            //3rd February 2017 was on Friday
            StringDate date = new StringDate(3, 2, 2017);

            Assert.IsFalse(date.isSunday());
        }
        public void TestCheckIfIsSundayReturnsTrueOnASundayDate()
        {
            //12nd February 2017 was on Sunday
            StringDate date = new StringDate(12, 2, 2017);

            Assert.IsTrue(date.isSunday());
        }