@Test
public void testReduce() {
Money dollar = Money.dollar(1);
Money reduce = dollar.reduce(new Bank(), dollar.currency());
assertEquals(dollar, reduce);
}
public Money reduce(Bank bank, String currency) {
Money from = augend.reduce(bank, currency);
Money to = addend.reduce(bank, currency);
return new Money(from.amount + to.amount, currency);
}