public void add_sli_with_same_product_will_change_quantity() { var sale = new Sale(); sale.AddLineItem(momogi, 2); Assert.AreEqual(1, sale.LineItems.Count); sale.AddLineItem(momogi); Assert.AreEqual(1, sale.LineItems.Count); var sli = sale.GetLineItem(momogi); Assert.AreEqual(3, sli.Quantity); }