@Test
public void testPlusReturnsSum() {
Expression five = Money.dollar(5);
Expression result = five.plus(five);
Sum sum = (Sum) result;
assertEquals(five, sum.augend);
assertEquals(five, sum.addend);
}
@Test
public void testSimpleAddition() {
Expression five = Money.dollar(5);
Expression sum = five.plus(five);
Bank bank = new Bank();
Money reduced = bank.reduce(sum, USD);
assertEquals(Money.dollar(10), reduced);
}