fsharp-testing

F# 測試模式

全面性的 F# 應用程式測試模式，涵蓋 xUnit、FsUnit、Unquote、FsCheck 以及現代化 .NET 測試實踐。

啟用時機

• 為 F# 程式碼撰寫新測試時
• 審查測試品質與涵蓋率時
• 為 F# 專案搭建測試基礎設施時
• 除錯不穩定或執行緩慢的測試時

測試框架工具鏈

工具	用途
xUnit	測試框架（.NET 生態系的標準首選）
FsUnit.xUnit	為 xUnit 提供符合 F# 語法習慣的斷言語法
Unquote	利用 F# 引號運算式（Quotations）的斷言函式庫，提供清晰的失敗訊息
FsCheck.xUnit	與 xUnit 整合的屬性導向測試（Property-based testing）
NSubstitute	Mock .NET 相依性
Testcontainers	在整合測試中使用真實的基礎設施
WebApplicationFactory	ASP.NET Core 整合測試

使用 xUnit + FsUnit 進行單元測試

基本測試結構

module OrderServiceTests

open Xunit
open FsUnit.Xunit

[<Fact>]
let ``create sets status to Pending`` () =
    let order = Order.create "cust-1" [ validItem ]
    order.Status |> should equal Pending

[<Fact>]
let ``confirm changes status to Confirmed`` () =
    let order = Order.create "cust-1" [ validItem ]
    let confirmed = Order.confirm order
    confirmed.Status |> should be (ofCase <@ Confirmed @>)

使用 Unquote 進行斷言

Unquote 採用 F# 引號運算式，因此測試失敗訊息會顯示完整的失敗運算式，而非僅僅提示「預期 X 但得到 Y」。

module OrderValidationTests

open Xunit
open Swensen.Unquote

[<Fact>]
let ``PlaceOrder returns success when request is valid`` () =
    let request = { CustomerId = "cust-123"; Items = [ validItem ] }
    let result = OrderService.placeOrder request
    test <@ Result.isOk result @>

[<Fact>]
let ``order total sums item prices`` () =
    let items = [ { Sku = "A"; Quantity = 2; Price = 10m }
                  { Sku = "B"; Quantity = 1; Price = 5m } ]
    let total = Order.calculateTotal items
    test <@ total = 25m @>

[<Fact>]
let ``validated email rejects empty input`` () =
    let result = ValidatedEmail.create ""
    test <@ Result.isError result @>

非同步測試

[<Fact>]
let ``PlaceOrder returns success when request is valid`` () = task {
    let deps = createTestDeps ()
    let request = { CustomerId = "cust-123"; Items = [ validItem ] }

    let! result = OrderService.placeOrder deps request

    test <@ Result.isOk result @>
}

[<Fact>]
let ``PlaceOrder returns error when items are empty`` () = task {
    let deps = createTestDeps ()
    let request = { CustomerId = "cust-123"; Items = [] }

    let! result = OrderService.placeOrder deps request

    test <@ Result.isError result @>
}

使用 Theory 進行參數化測試

[<Theory>]
[<InlineData("")>]
[<InlineData("   ")>]
let ``PlaceOrder rejects empty customer 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("user@example.com", true)>]
[<InlineData("user+tag@example.co.uk", true)>]
let ``IsValidEmail returns expected result`` (email: string, expected: bool) =
    test <@ EmailValidator.isValid email = expected @>

使用 FsCheck 進行屬性導向測試

使用 FsCheck.xUnit

open FsCheck
open FsCheck.Xunit

[<Property>]
let ``order total is always non-negative`` (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 ``serialization roundtrips`` (order: Order) =
    let json = JsonSerializer.Serialize order
    let deserialized = JsonSerializer.Deserialize<Order> json
    deserialized = order

自訂產生器

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 ``valid emails pass validation`` (email: string) =
    EmailValidator.isValid email

Mock 相依性

函式 Stub（推薦）

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 saves the confirmed order`` () = task {
    let mutable saved = []
    let deps =
        { createTestDeps () with
            SaveOrder = fun order -> task { saved <- order :: saved } }

    let! _ = OrderService.placeOrder deps validRequest

    test <@ saved.Length = 1 @>
}

針對 .NET 介面的 NSubstitute

open NSubstitute

[<Fact>]
let ``calls repository with correct ID`` () = 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 returns 404 when not found`` () = task {
        let! response = client.GetAsync($"/api/orders/{Guid.NewGuid()}")
        test <@ response.StatusCode = HttpStatusCode.NotFound @>
    }

測試組織架構

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

常見的反模式

反模式	修復方式
測試實作細節	測試行為與結果
可變的共享測試狀態	為每個測試提供獨立的全新狀態
在非同步測試中使用 Thread.Sleep	使用帶有逾時設定的 Task.Delay 或輪詢輔助函式
斷言 sprintf 的輸出	斷言強型別數值與模式比對結果
忽略 CancellationToken	務必傳遞並驗證取消行為
跳過屬性導向測試	對於具有明確不變量的函式，使用 FsCheck 進行測試

相關 Skills

• dotnet-patterns - 道地的 .NET 模式、相依性注入與架構
• csharp-testing - C# 測試模式（共用的基礎設施如 WebApplicationFactory 與 Testcontainers 也適用於 F#）

執行測試

# 執行所有測試
dotnet test

# 執行測試並收集程式碼涵蓋率
dotnet test --collect:"XPlat Code Coverage"

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

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

# 開發期間的 Watch 模式
dotnet watch test --project tests/MyApp.Tests/