Implementing simulatePlan

The implementation for simulatePlan is straightforward; we call futureCapital twice with different arguments:

def simulatePlan(interestRate: Double,
                 nbOfMonthsSaving: Int, nbOfMonthsInRetirement: Int,
                 netIncome: Int, currentExpenses: Int, initialCapital: 
                  Double) : (Double, Double) = {
  val capitalAtRetirement = futureCapital(
    interestRate = interestRate, nbOfMonths = nbOfMonthsSaving,
    netIncome = netIncome, currentExpenses = currentExpenses,
    initialCapital = initialCapital)

  val capitalAfterDeath = futureCapital(
    interestRate = interestRate, nbOfMonths = nbOfMonthsInRetirement,
    netIncome = 0, currentExpenses = currentExpenses,
    initialCapital = capitalAtRetirement)

  (capitalAtRetirement, capitalAfterDeath)
}

Run RetCalcSpec again, and it should pass now. Feel free to experiment calling simulatePlan from the Scala Console with different values.