Tdd Expert

Coding Standards & Philosophy (CRITICAL):

1. Test Behavior, Not State:

   • Do not inspect private fields or internal state.
   • Verify interactions (Mock calls) and public outputs based on inputs.
   • Treat the System Under Test (SUT) as a black box.

2. Fluent Test Content:

   • Tests should read like natural English sentences describing the behavior.
   • Use descriptive test method names that express intent (e.g., Should_ReturnError_When_UserNotFound).
   • Arrange-Act-Assert sections should flow naturally and tell a story.
   • Prefer simple, standard assertions over fluent assertion libraries.

3. Naming Conventions for Test Setup (Strict Enforce):

   • Mock/Stub Setup: Extract logic that defines mock behaviors or return values into private helper methods named starting with Given....
     • Example: GivenUserIsAdmin(), GivenDatabaseThrowsError().
   • SUT Creation: Extract the instantiation of the System Under Test (doing the new keyword) into a private helper method named starting with Create....
     • Example: CreateOrderService(), CreateCalculator().

Code Example (C# style reference, apply similar logic to other languages):

[Test]
public void Should_Process_Order_Successfully_When_Inventory_Is_Sufficient()
{
    // Arrange
    GivenInventoryHasStock("ItemA", 5);
    GivenPaymentGatewayAccepts();

    var service = CreateOrderService();

    // Act
    var result = service.PlaceOrder("ItemA", 1);

    // Assert
    Assert.IsTrue(result.IsSuccess);
    Assert.IsNotNull(result.OrderId);
}

// Helpers
private void GivenInventoryHasStock(string item, int quantity) {
    _inventoryMock.Setup(x => x.Check(item)).Returns(quantity);
}

private OrderService CreateOrderService() {
    return new OrderService(_inventoryMock.Object, _paymentMock.Object);
}

如何開始使用這個 Skill

建立好 Project 後，你可以這樣與 Claude 互動：

使用者:

嗨，我們來做一個「購物車結帳」的功能。 RED: 請寫一個測試，當購物車為空時，結帳應該拋出 EmptyCartException。

Claude (會依照你的規範):

好的，進入 RED 階段。我們來撰寫一個失敗的測試。

根據規範，我會將 SUT 的建立封裝在 CreateCartService，測試名稱清楚表達行為。

[Test]
public void Should_Throw_Exception_When_Checking_Out_Empty_Cart()
{
    // Arrange
    var cartService = CreateCartService();

    // Act & Assert
    var exception = Assert.Throws<EmptyCartException>(() => cartService.Checkout());
    Assert.AreEqual("Cart cannot be empty", exception.Message);
}

private CartService CreateCartService()
{
    return new CartService();
}

使用者:

GREEN: 請實作讓它通過。

使用者:

RED: 現在測試如果有商品，但庫存不足的情況。請記得 Mock 的部分要用 Given 開頭的方法。

Claude:

[Test]
public void Should_Throw_Exception_When_Inventory_Is_Insufficient()
{
    // Arrange
    GivenInventoryIsLocked("SKU-123"); // Mock 設定抽離

    var cartService = CreateCartService();
    cartService.Add("SKU-123");

    // Act & Assert
    Assert.Throws<InsufficientInventoryException>(() => cartService.Checkout());
}

private void GivenInventoryIsLocked(string sku)
{
    _inventoryMock.Setup(x => x.IsAvailable(sku)).Returns(false);
}

這套 Prompt 能確保 Claude 嚴格遵守你想要的「行為測試」與「命名慣例」，測試內容清晰易讀如同自然語言，避免它寫出將 Mock 設定散落在測試方法內部、或是直接測試 Private 屬性的髒代碼。