Listing 2. Modify the getMortgageResponse() method until the JUnit test cases succeed. This is how the code looks when the JUnit test cases begin to pass.

/*
            rL(1 + r/12)^(12N)
     P =  -----------------------
          12((1 + r/12)^(12N) - 1)

where:
      r = interest rate (for 8.25% ==> r = 0.0825)
      L = loan amount 
      N = loan time (years)
      P = the monthly payment
*/
protected int getMortgageResponse(
  PaymentInfo paymentInfo) {
    double amount = paymentInfo.getHomePrice() - 
                    paymentInfo.getDownPayment();
    int years = paymentInfo.getYears();
    double rate = paymentInfo.getInterestRate()/100;
    double base = (double)(1 + rate/12);
    double exponent = (double)(12 * years);
    double result = java.lang.Math.pow(base, exponent);
    double numerator = rate * amount * result;
    double denominator = 12 * (result - 1);
    int monthlyPayment = (int)(
      numerator / denominator);
    return monthlyPayment;
}