.Nettuce

    public static class DateTimeProvider
    {
        static Func<DateTime> nowFunc = () => DateTime.UtcNow;

        public static DateTime Now
        {
            get { return nowFunc(); }
            set { nowFunc = () => value; }
        }
    }

By default it returns DateTime.UtcNow; override in your tests by calling

DateTimeProvider.Now = DateTime.Today;