public void Add_Year()
        {
            var startDate = new ApproximateDateTime();

            startDate.AddYears(3);

            Assert.Equal(startDate.Year, 3);
        }
        public void Subtract_Year()
        {
            var startDate = new ApproximateDateTime();

            startDate.AddYears(-3);

            Assert.Equal(startDate.Year, -3);
        }