swift-testing

Swift Testing

Instructions

Step 1: Determine Testing Mode

Check CLAUDE.md for Testing Mode:

• enterprise → consult references/enterprise.md for strict rules
• indie → consult references/indie.md for pragmatic rules
• If not set: ask the user which mode applies

Step 2: Identify What to Test

Ask if not already clear:

• Which type / function / feature needs tests?
• What is the expected behavior (not implementation)?
• Are there async operations?
• Are there existing mocks or does the skill need to create them?

Always test:

• ViewModels (state changes, actions, error states)
• Services and Repositories (business logic, data transformations)
• Formatters, validators, utilities
• Async flows end-to-end (with mocked dependencies)
• Edge cases and error paths

Never test:

• Private implementation details
• SwiftUI view tree structure or layout positions
• UIViewController internal wiring

Step 3: Choose the Framework

Scenario	Framework
New unit tests (Swift 5.9+, iOS 16+)	Swift Testing (@Test, #expect)
Legacy or team convention on XCTest	XCTest (XCTestCase, XCTAssert*)
UI / end-to-end tests	XCTest + XCUITest
Async unit tests	Both support async — use await

Do NOT mix Swift Testing and XCTest in the same test target.

Step 4: Write Tests

Naming (both frameworks):

test_when_<Condition>_should_<ExpectedOutcome>()

Structure — Swift Testing:

import Testing
@testable import MyApp

@MainActor
struct LoginViewModelTests {

    @Test func test_when_credentialsAreValid_should_setIsLoggedIn() async throws {
        // Arrange
        let authService = MockAuthService(willSucceed: true)
        let sut = LoginViewModel(authService: authService)

        // Act
        await sut.login(email: "[email protected]", password: "secret")

        // Assert
        #expect(sut.isLoggedIn == true)
        #expect(sut.error == nil)
    }

    @Test func test_when_credentialsAreInvalid_should_setError() async throws {
        // Arrange
        let authService = MockAuthService(willSucceed: false)
        let sut = LoginViewModel(authService: authService)

        // Act
        await sut.login(email: "[email protected]", password: "wrong")

        // Assert
        #expect(sut.isLoggedIn == false)
        #expect(sut.error != nil)
    }
}