@Test
 public void testSetQuantity() {
   freshWater.setQuantity(85);
   assertEquals(85, freshWater.getQuantity());
   ultraBall.setQuantity(50);
   assertEquals(50, ultraBall.getQuantity());
 }
 @Test
 public void testGetQuantity() {
   assertEquals(2, ultraBall.getQuantity());
   assertEquals(100, freshWater.getQuantity());
   assertEquals(40, maxRevive.getQuantity());
 }