public void testTwoCards() {
   Billfold wallet = new Billfold(new Card(), new Card());
   assertEquals(
       "[" + wallet.getCard1().format() + "|" + wallet.getCard2().format() + "]",
       wallet.formatCard());
 }
 public void testOneCard() {
   Billfold wallet = new Billfold(new Card());
   assertEquals("[" + wallet.getCard1().format() + "|null]", wallet.formatCard());
 }