swift-testing

Swift Testing

Author tests with the modern Swift Testing framework (import Testing, Xcode 16+/Swift 6). It coexists with XCTest in the same target — migrate incrementally. For the test harness, CI wiring, SwiftData in-memory setup, and UI/performance testing, see ios-test; this skill is the authoring model.

Pick the right tool. Swift Testing covers unit/integration/logic tests. UI tests (XCUIApplication) and XCTMetric performance tests still use XCTest — Swift Testing does not replace them. You can keep both in one project.

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The shape of a test

import Testing
@testable import MyApp

@Test func timerStartsAtConfiguredDuration() {
    let timer = FocusTimer(minutes: 25)
    #expect(timer.remaining == .seconds(25 * 60))
}

• No XCTest subclass, no test prefix, no XCTAssert. A free function (or method) annotated @Test.
• #expect(...) records a failure but continues. It captures the full expression, so #expect(a == b) reports the actual values of a and b — no need for XCTAssertEqual.
• Give tests descriptive names: @Test("Remaining time is clamped to zero").

#require — stop on failure / safe unwrap

@Test func decodesUser() throws {
    let data = try #require(Self.fixture)         // unwraps Optional or throws → test stops
    let user = try JSONDecoder().decode(User.self, from: data)
    #expect(user.name == "Ada")
}

#require is the hard assert: if it fails the test stops (like a guard). Use it when continuing would crash or cascade. try #require(optional) is the idiomatic non-force unwrap.

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Async, throwing, and errors

@Test func loadsRemoteProfile() async throws {
    let profile = try await client.fetchProfile(id: 42)   // just use async/await
    #expect(profile.id == 42)
}

// Asserting a specific error is thrown
@Test func rejectsEmptyName() {
    #expect(throws: ValidationError.emptyName) {
        try Validator.validate(name: "")
    }
}

// Any error / error of a type
#expect(throws: (any Error).self) { try risky() }
#expect(throws: ValidationError.self) { try validate() }
#expect(throws: Never.self) { try shouldNotThrow() }   // asserts NO throw