Swift Testing

Swift Testing is Apple's modern testing framework (WWDC 2024). It uses macros (@Test, #expect), runs tests in parallel, and integrates with Swift concurrency.

When to Use

Use this skill when:

• Writing unit tests with Swift Testing
• Making tests run faster (without simulator)
• Testing async code reliably
• Migrating from XCTest
• Deciding between Swift Testing and XCTest

Example Prompts

• "How do I write a unit test with Swift Testing?"
• "My tests take 60 seconds — how do I make them faster?"
• "How do I test async code without flaky failures?"
• "Should I use Swift Testing or XCTest?"
• "How do I migrate from XCTest?"

What This Skill Provides

Basic Structure

import Testing

@Test func videoHasCorrectMetadata() {
    let video = Video(named: "example.mp4")
    #expect(video.duration == 120)
}

The Speed Hierarchy

Configuration	Time	Use Case
swift test (Package)	~0.1s	Pure logic, models
Host Application: None	~3s	Framework code
Full app launch	20-60s	UI tests

Key insight: Move testable logic into Swift Packages, then test with swift test.

Async Testing

@Test func notificationReceived() async {
    await confirmation(expectedCount: 1) { confirm in
        NotificationCenter.default.addObserver(...) {
            confirm()
        }
        triggerNotification()
    }
}

XCTest Migration

XCTest	Swift Testing
func testFoo()	@Test func foo()
XCTAssertEqual(a, b)	#expect(a == b)
XCTUnwrap(x)	try #require(x)
class Tests: XCTestCase	@Suite struct Tests

Keep XCTest for: UI tests, performance tests, Objective-C.

Parameterized Tests

@Test(arguments: [IceCream.vanilla, .chocolate, .strawberry])
func flavorWithoutNuts(_ flavor: IceCream) {
    #expect(!flavor.containsNuts)
}

Related

• ui-testing — UI testing with Recording UI Automation
• swift-concurrency — Async patterns for testing

Resources

WWDC: 2024-10179 (Meet Swift Testing), 2024-10195 (Go further)

Docs: /documentation/testing

Point-Free: swift-concurrency-extras, swift-clocks