@Test
 public void sub_basket_set_collection_should_be_empty() {
   BasketSuite suite = new BasketSuite();
   assertThat(suite.getSubBasketSets().isEmpty(), is(true));
 }
 @Test
 public void sub_basket_set_collection_should_has_only_one_item() {
   BasketSuite suite = new BasketSuite();
   suite.addBook("first", 1);
   assertThat(suite.getSubBasketSets().size(), is(1));
 }