更新我們的AddItemCommand多增加一個SessionId欄位用於配置GUID唯一識別

public class AddItemCommand
{
    public int ProductId { get; set; }
    public Guid? SessionId { get; set; }
}

新增一個AddItemResult的DTO

public class AddItemResult
{
    public Guid SessionId { get; set; }
}

調整CartService封裝的AddItem改為具有返回值型態為AddItemResult

public AddItemResult AddItem(AddItemCommand command)
        {
            // if sessionId is provided, look it up
            // add item to the existing cart
            // return existing cart sessionId
            ShoppingCart cart;

            if (command.SessionId.HasValue)
            {
                cart = dbContext.ShoppingCart.SingleOrDefault(x => x.SessionId == command.SessionId);
            } else
            {
                Guid newCartSessionId = Guid.NewGuid();
                cart = new ShoppingCart { SessionId = newCartSessionId, CreatedOn = DateTime.Now };
                dbContext.ShoppingCart.Add(cart);
            }
                        
            cart.Items.Add(new CartLineItem { ProductId = command.ProductId, Quantity = 1 });           
            dbContext.SaveChanges();

            return new AddItemResult { SessionId = cart.SessionId };
        }
    }

微調CartController的AddItem方法

[HttpPost]
public IActionResult AddItem(AddItemCommand command)
{
    var result = cartService.AddItem(command);
    return Ok(result);
}

這裡使用XUnit (跟其他兩牌用法其實差異不大)

相應比較對照表

在此會採用到UseInMemoryDatabase記憶體中產生一個暫時性DB用於for單元測試進行臨時性的驗證
單元測試要求的重點
不和外部資源(DB,WebService,web api,檔案系統…)相關聯，通常
又被稱作「隔離測試」(Ex:即便在離線環境也要能夠測試跟api呼叫或DB存取有關的unit test)

Install-Package Microsoft.EntityFrameworkCore.InMemory -Version 3.1.5

public class AddItemToCartShould
    {
        private DbContextOptions<StoreContext> options;

        public AddItemToCartShould()
        {
            options = new DbContextOptionsBuilder<StoreContext>()
                .UseInMemoryDatabase(databaseName: "Cart")
                .Options;
        }

        [Fact]
        public void CreateCartIfNotFound()
        {
            using (var context = new StoreContext(options))
            {
                var cartService = new CartService(context);
                var result = cartService.AddItem(new AddItemCommand { ProductId = 1, SessionId = null });
                Assert.NotEqual(Guid.Empty, result.SessionId);
            }
        }

        [Fact]
        public void NotCreateCartIfExistingOneFound()
        {
            Guid sessionId = Guid.NewGuid();

            using (var context = new StoreContext(options))
            {
                context.ShoppingCart.Add(new ShoppingCart { SessionId = sessionId });
                context.SaveChanges();
            }

            using (var context = new StoreContext(options))
            {
                var cartService = new CartService(context);
                var result = cartService.AddItem(new AddItemCommand { ProductId = 1, SessionId = sessionId });
                Assert.Equal(sessionId, result.SessionId);
            }
        }
    }

再次我們要進行的驗證就是確保session每一次只獲取一個購物車