### Question:
MoneyBag implements IMoney { public boolean isZero() { return fMonies.size() == 0; }  IMoney add(IMoney m); IMoney addMoney(Money m); IMoney addMoneyBag(MoneyBag s); boolean equals(Object anObject); int hashCode(); boolean isZero(); IMoney multiply(int factor); IMoney negate(); IMoney subtract(IMoney m); String toString(); void appendTo(MoneyBag m);  }### Answer:
@Test public void testIsZero() { assertTrue(fMB1.subtract(fMB1).isZero()); assertTrue(MoneyBag.create(new Money(0, "CHF"), new Money(0, "USD")).isZero()); }