public void AddCartItem_GivenCartAndProduct_ThenProductShouldBeAddedToCart() { int cartItemId = 42, cartId = 1, userId = 33, productId = 777; //Stub ICartSaver and customize the behavior via a //delegate, ro return cartItemId var cartSaver = new Fakes.StubICartSaver(); cartSaver.SaveCartItemInt32Int32 = (c, p) => cartItemId; var cart = new CartToStub(cartId, userId, cartSaver); cart.AddCartItem(productId); Assert.AreEqual(cartId, cart.CartItems.Count); var cartItem = cart.CartItems[0]; Assert.AreEqual(cartItemId, cartItem.CartItemId); Assert.AreEqual(productId, cartItem.ProductId); }