public void DispensesChangeNickelsAndDimes(decimal change, int expectedNumberOfDimes, int expectedNumberOfNickels)
        {
            var system = new VendingSystem(products, bankedCoins);

            system.CalculateChangeInCoins(change);
            var nickels = system.CoinsToDispense.Where(coins => coins.Key == CoinType.Nickel).FirstOrDefault();
            var dimes   = system.CoinsToDispense.Where(coins => coins.Key == CoinType.Dime).FirstOrDefault();

            Assert.Equal(expectedNumberOfNickels, nickels.Value);
            Assert.Equal(expectedNumberOfDimes, dimes.Value);
        }