fsharp-testing

F# 測試模式

適用於 F# 應用程式的完整測試模式，使用 xUnit、FsUnit、Unquote、FsCheck 與現代 .NET 測試實務。

何時啟用

• 為 F# 程式碼撰寫新的測試
• 審查測試品質與涵蓋率
• 為 F# 專案設定測試基礎設施
• 偵錯不穩定或緩慢的測試

測試框架堆疊

工具	用途
xUnit	測試框架（標準 .NET 生態系統選擇）
FsUnit.xUnit	為 xUnit 提供 F# 友善的斷言語法
Unquote	使用 F# 引號（quotations）的斷言函式庫，提供清晰的失敗訊息
FsCheck.xUnit	與 xUnit 整合的屬性測試
NSubstitute	模擬 .NET 相依性
Testcontainers	在整合測試中使用真實基礎設施
WebApplicationFactory	ASP.NET Core 整合測試

使用 xUnit + FsUnit 的單元測試

基本測試結構

module OrderServiceTests

open Xunit
open FsUnit.Xunit

[<Fact>]
let ``建立後狀態設為 Pending`` () =
    let order = Order.create "cust-1" [ validItem ]
    order.Status |> should equal Pending

[<Fact>]
let ``確認後狀態變更為 Confirmed`` () =
    let order = Order.create "cust-1" [ validItem ]
    let confirmed = Order.confirm order
    confirmed.Status |> should be (ofCase <@ Confirmed @>)

使用 Unquote 的斷言

Unquote 使用 F# 引號，因此失敗訊息會顯示失敗的完整運算式，而不僅僅是「預期 X 得到 Y」。

module OrderValidationTests

open Xunit
open Swensen.Unquote

[<Fact>]
let ``PlaceOrder 在請求有效時回傳成功`` () =
    let request = { CustomerId = "cust-123"; Items = [ validItem ] }
    let result = OrderService.placeOrder request
    test <@ Result.isOk result @>

[<Fact>]
let ``訂單總金額為各項目價格總和`` () =
    let items = [ { Sku = "A"; Quantity = 2; Price = 10m }
                  { Sku = "B"; Quantity = 1; Price = 5m } ]
    let total = Order.calculateTotal items
    test <@ total = 25m @>

[<Fact>]
let ``驗證電子郵件拒絕空白輸入`` () =
    let result = ValidatedEmail.create ""
    test <@ Result.isError result @>

非同步測試

[<Fact>]
let ``PlaceOrder 在請求有效時回傳成功`` () = task {
    let deps = createTestDeps ()
    let request = { CustomerId = "cust-123"; Items = [ validItem ] }

    let! result = OrderService.placeOrder deps request

    test <@ Result.isOk result @>
}

[<Fact>]
let ``PlaceOrder 在項目清單為空時回傳錯誤`` () = task {
    let deps = createTestDeps ()
    let request = { CustomerId = "cust-123"; Items = [] }

    let! result = OrderService.placeOrder deps request

    test <@ Result.isError result @>
}

使用 Theory 的參數化測試

[<Theory>]
[<InlineData("")>]
[<InlineData("   ")>]
let ``PlaceOrder 拒絕空的客戶 ID`` (customerId: string) =
    let request = { CustomerId = customerId; Items = [ validItem ] }
    let result = OrderService.placeOrder request
    result |> should be (ofCase <@ Error @>)

[<Theory>]
[<InlineData("", false)>]
[<InlineData("a", false)>]
[<InlineData("[email protected]", true)>]
[<InlineData("[email protected]", true)>]
let ``IsValidEmail 回傳預期結果`` (email: string, expected: bool) =
    test <@ EmailValidator.isValid email = expected @>

使用 FsCheck 的屬性測試

使用 FsCheck.xUnit

open FsCheck
open FsCheck.Xunit

[<Property>]
let ``訂單總金額永遠非負`` (items: NonEmptyList<PositiveInt * decimal>) =
    let orderItems =
        items.Get
        |> List.map (fun (qty, price) ->
            { Sku = "SKU"; Quantity = qty.Get; Price = abs price })
    let total = Order.calculateTotal orderItems
    total >= 0m

[<Property>]
let ``序列化往返`` (order: Order) =
    let json = JsonSerializer.Serialize order
    let deserialized = JsonSerializer.Deserialize<Order> json
    deserialized = order

自訂生成器

type OrderGenerators =
    static member ValidEmail () =
        gen {
            let! user = Gen.elements [ "alice"; "bob"; "carol" ]
            let! domain = Gen.elements [ "example.com"; "test.org" ]
            return $"{user}@{domain}"
        }
        |> Arb.fromGen

[<Property(Arbitrary = [| typeof<OrderGenerators> |])>]
let ``有效的電子郵件通過驗證`` (email: string) =
    EmailValidator.isValid email

模擬相依性

函式樁（偏好做法）

let createTestDeps () =
    let mutable savedOrders = []
    { FindOrder = fun id -> task { return Map.tryFind id testData }
      SaveOrder = fun order -> task { savedOrders <- order :: savedOrders }
      SendNotification = fun _ -> Task.CompletedTask }

[<Fact>]
let ``PlaceOrder 儲存已確認的訂單`` () = task {
    let mutable saved = []
    let deps =
        { createTestDeps () with
            SaveOrder = fun order -> task { saved <- order :: saved } }

    let! _ = OrderService.placeOrder deps validRequest

    test <@ saved.Length = 1 @>
}

使用 NSubstitute 模擬 .NET 介面

open NSubstitute

[<Fact>]
let ``使用正確的 ID 呼叫儲存庫`` () = task {
    let repo = Substitute.For<IOrderRepository>()
    repo.FindByIdAsync(Arg.Any<Guid>(), Arg.Any<CancellationToken>())
        .Returns(Task.FromResult(Some testOrder))

    let service = OrderService(repo)
    let! _ = service.GetOrder(testOrder.Id, CancellationToken.None)

    do! repo.Received(1).FindByIdAsync(testOrder.Id, Arg.Any<CancellationToken>())
}

ASP.NET Core 整合測試

type OrderApiTests (factory: WebApplicationFactory<Program>) =
    interface IClassFixture<WebApplicationFactory<Program>>

    let client =
        factory.WithWebHostBuilder(fun builder ->
            builder.ConfigureServices(fun services ->
                services.RemoveAll<DbContextOptions<AppDbContext>>() |> ignore
                services.AddDbContext<AppDbContext>(fun options ->
                    options.UseInMemoryDatabase("TestDb") |> ignore) |> ignore))
            .CreateClient()

    [<Fact>]
    member _.``GET order 在找不到時回傳 404`` () = task {
        let! response = client.GetAsync($"/api/orders/{Guid.NewGuid()}")
        test <@ response.StatusCode = HttpStatusCode.NotFound @>
    }

測試組織

tests/
  MyApp.Tests/
    Unit/
      OrderServiceTests.fs
      PaymentServiceTests.fs
    Integration/
      OrderApiTests.fs
      OrderRepositoryTests.fs
    Properties/
      OrderPropertyTests.fs
    Helpers/
      TestData.fs
      TestDeps.fs

常見反模式

反模式	修正建議
測試實作細節	測試行為與結果
可變的共享測試狀態	每個測試使用全新狀態
在非同步測試中使用 Thread.Sleep	使用 Task.Delay 搭配逾時，或輪詢輔助程式
對 sprintf 輸出進行斷言	對型別值與模式比對進行斷言
忽略 CancellationToken	始終傳遞並驗證取消
跳過屬性測試	對任何具有明確不變量的函式使用 FsCheck

相關技能

• dotnet-patterns - 慣用的 .NET 模式、相依性注入與架構
• csharp-testing - C# 測試模式（WebApplicationFactory 和 Testcontainers 等共享基礎設施也適用於 F#）

執行測試

# 執行所有測試
dotnet test

# 執行測試並收集涵蓋率
dotnet test --collect:"XPlat Code Coverage"

# 執行特定專案的測試
dotnet test tests/MyApp.Tests/

# 依測試名稱篩選
dotnet test --filter "FullyQualifiedName~OrderService"

# 開發期間監看模式
dotnet watch test --project tests/MyApp.Tests/