public static void main(String[] args) {
        // Create an empty billfold
        Billfold b = new Billfold();
        System.out.println("**Actual: ");
        System.out.println(b);
        System.out.println("**Expected: ");
        System.out.println("Billfold:\nempty\nempty\nempty\n");

        // Create two Card objects
        IDCard card1 = new IDCard("Mary Kay", "1234567");
        CallingCard card2 = new CallingCard("Omega Card", "301233985945", 1030);
        b.addCard(card1);
        b.addCard(card2);
        System.out.println("**Actual: ");
        System.out.println(b);
        System.out.println("**Expected: ");
        System.out.println("Billfold:\nID[name: Mary Kay, id:1234567]\n"
                + "Calling Card[name: Omega Card, Card #:301233985945, pin: 1030]\n"
                + "empty\n");

        // create another card       
        DriverLicense card3 = new DriverLicense("John Doe", "08-097654", 2007);
        b.addCard(card3);
        System.out.println("**Actual: ");
        System.out.println(b);
        System.out.println("**Expected: ");
        System.out.println("Billfold:\n"
                + "ID[name: Mary Kay, id:1234567]\n"
                + "Calling Card[name: Omega Card, Card #:301233985945, pin: 1030]\n"
                + "Driver's License[ ID[name: John Doe, id:08-097654], expYear: 2007]\n");
    }