public void AddItemPromotionTest_addDuplicatePromotion_exceptionExpected() {
     PromotionModel model = new PromotionModel(new string[0]);
     Item item = new Item("Apple");
     Dictionary<Item, Promotion> existingDictionary = new Dictionary<Item, Promotion>();
     existingDictionary.Add(item, new QuantityPricePromotion(item, "[email protected]"));
     model.AddItemPromotion(existingDictionary, "Apple,QtyPromoPrice,[email protected]");
 }
 public void AddItemPromotionTest_addPromotion_itemAddedToDictionary() {
     PromotionModel model = new PromotionModel(new string[0]);
     Item item = new Item("Apple");
     Dictionary<Item, Promotion> existingDictionary = new Dictionary<Item, Promotion>();            
     model.AddItemPromotion(existingDictionary, "Apple,QtyPromoPrice,[email protected]");
     Assert.AreEqual(1, existingDictionary.Count);
     Assert.IsTrue(existingDictionary.ContainsKey(item));
     Assert.IsTrue(existingDictionary[item] is QuantityPricePromotion);
 }