public void testSubtractFundsActuallyRemovesCorrectFundsToBalanceValue() throws Exception {
    UserBalanceInterface userBalance = new UserBalance();

    userBalance.addFunds(InsertedCoinPiece.QUARTER);
    userBalance.addFunds(InsertedCoinPiece.QUARTER);
    userBalance.addFunds(InsertedCoinPiece.DIME);

    double expectedUserBalanceAsFractionOfDollar = .60;
    assertEquals(expectedUserBalanceAsFractionOfDollar, userBalance.getBalanceValue());

    userBalance.subtractFunds(".50");
    double expectedUserBalanceAsFractionOfDollarAfterSubtractingFunds = .10;
    assertEquals(
        expectedUserBalanceAsFractionOfDollarAfterSubtractingFunds, userBalance.getBalanceValue());
  }
 public void testAddFundsActuallyAddsCorrectFundsToBalanceValue() throws Exception {
   UserBalanceInterface userBalance = new UserBalance();
   userBalance.addFunds(InsertedCoinPiece.QUARTER);
   double expectedBalanceValueAsFractionOfADollar = .25;
   assertEquals(
       "Make certain that the conversion to fraction of a dollar is .01!",
       expectedBalanceValueAsFractionOfADollar,
       userBalance.getBalanceValue());
 }