public void TimePeriod_Diff(byte h1, byte m1, byte s1,
                                    byte h2, byte m2, byte s2,
                                    byte h3, byte m3, byte s3)
        {
            TimePeriod tp1        = new TimePeriod(h1, m1, s1);
            TimePeriod tp2        = new TimePeriod(h2, m2, s2);
            TimePeriod tpExpected = new TimePeriod(h3, m3, s3);

            Assert.AreEqual(tp1.Difference(tp2), tpExpected);
        }