public void CallDuration_TwentyCentsCallCost312_CallDurationFourteenMinutes()
        {
            PhoneCall phoneCall = new PhoneCall(3, 1, 2, 20);

            Assert.AreEqual(14, phoneCall.CallDuration());
        }
        public void CallDuration_FiftySixCentsCallCost523_CallDurationTwentOneMinutes()
        {
            PhoneCall phoneCall = new PhoneCall(5, 2, 3, 55);

            Assert.AreEqual(21, phoneCall.CallDuration());
        }