public void Can_add_more_to_boxed_item_quantity()
        {
            var item = new Item();
            var boxedItem = new BoxedItem(1, item);

            Assert.Equal(1, boxedItem.Quantity);

            boxedItem.AddMore(1);

            Assert.Equal(2, boxedItem.Quantity);
        }
 public void Trying_to_add_negative_number_throws_error()
 {
     var boxedItem = new BoxedItem(1, new Item());
     Assert.Throws<InvalidOperationException>(() => boxedItem.AddMore(-1));
 }