public void TestNextYearsInterestRate_Equals_ThisYearsInterestRate()
        {
            SavingsAccountYear thisYear = NewAccount();

            Assert.AreEqual(thisYear.InterestRate(), thisYear.NextYear().InterestRate());
        }
        public void TestNextYearsStartingBalance_Equals_ThisYearsEndingBalance()
        {
            SavingsAccountYear thisYear = NewAccount();

            Assert.AreEqual(thisYear.EndingBalance(), thisYear.NextYear().StartingBalance());
        }