@Test
    public void testToString() {
        AbstractCardCollection collection = new AbstractCardCollectionImpl(2);  
        
        assertTrue(collection.addCard(new Card(Suit.CLUB, Rank.ACE)));      
        assertTrue(collection.addCard(new Card(Suit.SPADE, Rank.ACE)));  
        
        String expected1 = "[Ac, As]";
        String expected2 = "[As, Ac]";
        
        String toString = collection.toString();
        
        if (!toString.equals(expected1) && !toString.equals(expected2)) {
            fail("toString method doesn't work correctly");
        }
    }