# WWDC 2024 - 了解 Swift Testing

- URL: https://www.rayzhao.work/posts/wwdc2024-swift-testing/
- Published: 2024-06-13
- Tags: Swift, iOS, WWDC
- Source: src/pages/posts/wwdc2024-swift-testing.mdx

> 介绍 WWDC 2024 推出的 Swift Testing，包括核心语法、断言方式，以及它与 XCTest 的关键差异。

## Building Block

```swift
import Testing
@testable import DestinationVideo

@Test("Check video metadata") func videoMetaData() {
    let video = Video(fileName: "By the Lake.mov")
    let expectedMetadata = Metadata(duration: .seconds(90))
    #expect(video.metadata == expectedMetadata)
}
```

`@Test` 宏用来标记这个函数是用来测试的；

默认访问修饰符是 internal，范围为整个 module，`@testable` 相当于可以解除这个禁制，让测试访问到。

`#expect` 宏用来测试条件是否为真

`#require` 宏用来断言，如果条件为假，会直接抛出异常，立即停止测试

```swift
try #require(session.isValid)

session.invalidate() // not executed
```


也可以用来断言可选类型，当空时退出测试

```swift
let method = try #require(paymentMethods.first)

#expect(method.isDefault) // not executed
```


## Traits

- 展示测试描述

- 定制测试用例什么时候跑，是否跑

- 修改测试用例执行的行为

一些内置的 Traits，更多详见[文档](https://developer.apple.com/documentation/testing/traits)

## Test Suite

可以将关联的测试函数放在一起，使用 @Suite 宏，可以有实例变量，也可以使用 init 和 deinit 来添加初始化与销毁的一些逻辑

```swift
struct VideoTests {

    @Test("Check video metadata") func videoMetadata() {
        let video = Video(fileName: "By the Lake.mov")
        let expectedMetadata = Metadata(duration: .seconds(90))
        #expect(video.metadata == expectedMetadata)
    }

    @Test func rating() async throws {
        let video = Video(fileName: "By the Lake.mov")
        #expect(video.contentRating == "G")
    }

}
```


`@Suite` 实例为每一个 `@Test` 方法都初始化一个新的防止状态共享。所以上面的代码可以改写成：

```swift
struct VideoTests {
    let video = Video(fileName: "By the Lake.mov")

    @Test("Check video metadata") func videoMetadata() {
        let expectedMetadata = Metadata(duration: .seconds(90))
        #expect(video.metadata == expectedMetadata)
    }

    @Test func rating() async throws {
        #expect(video.contentRating == "G")
    }

}
```


## Common workflows

运行时条件 Runtime conditions，用来控制测试什么时候跑。

`.enabled(if: ...)` ，当条件为 false 时会跳过测试

```swift
@Test(.enabled(if: AppFeatures.isCommentingEnabled)) // Test 'videoCommenting()' skipped
func videoCommenting() {
    // ...
}
```


`.disabled(...)` ，可以描述为什么这个测试被禁用

```swift
@Test(.disabled("Due to a known crash"))
func example() {
    // ...
}
```

`.bug(...)`，可以用来关联一个 issue

```swift
@Test(.disabled("Due to a known crash"), .bug("example.org/bugs/1234", "Program crashes at <symbol>"))
func example() {
    // ...
}
```


可以基于操作系统版本可用性来作为条件，使用 `.available(...)` 而不是 `#available(...)`

```swift
// Not recommend
@Test func hasRuntimeVersionCheck() {
    guard #available(macOS 15, *) else { return }
}

@Test
@available(macOS 15, *)
func usesNewAPIs() {
    // ...
}
```


使用 `.tags(...)` 来给测试添加标签，用来分组，方便在 Xcode 中根据标签分组查看

带参数的测试 parameterized testing，使用 arguments

```swift
// Before
struct VideoContinentsTests {

    @Test func mentionsFor_A_Beach() async throws {
        let videoLibrary = try await VideoLibrary()
        let video = try #require(await videoLibrary.video(named: "A Beach"))
        #expect(!video.mentionedContinents.isEmpty)
        #expect(video.mentionedContinents.count <= 3)
    }

    @Test func mentionsFor_By_the_Lake() async throws {
        let videoLibrary = try await VideoLibrary()
        let video = try #require(await videoLibrary.video(named: "By the Lake"))
        #expect(!video.mentionedContinents.isEmpty)
        #expect(video.mentionedContinents.count <= 3)
    }

    @Test func mentionsFor_Camping_in_the_Woods() async throws {
        let videoLibrary = try await VideoLibrary()
        let video = try #require(await videoLibrary.video(named: "Camping in the Woods"))
        #expect(!video.mentionedContinents.isEmpty)
        #expect(video.mentionedContinents.count <= 3)
    }

    // ...and more, similar test functions
}

// After
struct VideoContinentsTests {

    @Test("Number of mentioned continents", arguments: [
        "A Beach",
        "By the Lake",
        "Camping in the Woods",
        "The Rolling Hills",
        "Ocean Breeze",
        "Patagonia Lake",
        "Scotland Coast",
        "China Paddy Field",
    ])
    func mentionedContinentCounts(videoName: String) async throws {
        let videoLibrary = try await VideoLibrary()
        let video = try #require(await videoLibrary.video(named: videoName))
        #expect(!video.mentionedContinents.isEmpty)
        #expect(video.mentionedContinents.count <= 3)
    }

}
```


## Swift Testing and XCTest

XCTest 与 Swift Testing 的对比:

更多信息可以查看Migrating a test from XCTest

## Open Source

全平台支持，SPM 命令行、Xcode、VSCode Swift Extension

Command line: swift test

## 其他信息

- 原视频：https://developer.apple.com/wwdc24/10179

- Github：https://github.com/apple/swift-testing

- 其他相关：利用 Swift Testing 进一步优化测试