public void Mortgage_CalculateMonthlyPayment()
        {
            // Arrange
            const int term = 5;
            const TermUnits termUnits = TermUnits.Years;
            const decimal principal = 100000M;
            const decimal annualPercentInterest = 6.0M;
            const decimal expectedMonthlyPayment = 1933.28M;
            var mortgage = new Mortgage
            {
                Principal = principal,
                AnnualPercentInterest = annualPercentInterest,
                Term = term,
                TermUnits = termUnits
            };

            // Act
            decimal monthlyPayment = mortgage.CalculateMonthlyPayment();

            // Assert
            Assert.AreEqual(expectedMonthlyPayment, monthlyPayment);
        }
 // POST api/monthlypayment
 public decimal Post(Mortgage mortgage)
 {
     return mortgage.CalculateMonthlyPayment();
 }