mock DateTime example

mockNow.cs

        [TestMethod]
        public void TestMethod1()
        {
            //arrange
            var p = new Person();

            MockContext.MockNow = new DateTime(2011, 1, 1);

            var result = p.Cal();


        }


    public class Person
    {
        internal long Cal()
        {
            //return DateTime.Now.Ticks;

            return MockContext.MockNow.Ticks;
        }
    }

    public static class MockContext
    {
        private static DateTime? _now;
        public static DateTime MockNow
        {
            get
            {
                if (_now == null)
                {
                    _now = DateTime.Now;
                }
                return (DateTime)_now;

            }
            set
            {
                _now = value;
            }
        }
    }