public void TimeSpanExtMillisecondTest_subtraction_operator()
        {
            DateTime dt = new DateTime(2000, 1, 1, 0, 0, 2, 222);
              int value = 2222;
              TimeSpanExtMillisecond edt = new TimeSpanExtMillisecond(value);
              DateTime expected = new DateTime(2000, 1, 1);

              DateTime actual;
              actual = dt - edt;

              Assert.AreEqual(expected, actual);
        }
        public void Subtraction_from_TimeSpanExtBase_returns_a_valid_TimeSpanExtBase()
        {
            DateTime dt = new DateTime(2000, 1, 1, 0, 0, 0, 0);
              TimeSpanExtMillisecond edt = new TimeSpanExtMillisecond(3);
              TimeSpanExtMillisecond edt2 = new TimeSpanExtMillisecond(2);
              DateTime expected = new DateTime(2000, 1, 1, 0, 0, 0, 1);

              TimeSpanExt composite = edt - edt2;

              DateTime actual;
              actual = dt + composite;

              Assert.AreEqual(expected, actual);
        }