ios-testing

iOS Testing

Testing patterns for Swift and SwiftUI apps.

Prefer the Swift Testing framework (Xcode 16+) for new unit tests; XCTest is still required for UI tests (XCUITest) and performance measurement.

Swift Testing

import Testing
@testable import MyApp

// @Test replaces test-prefixed methods; the name is a plain description.
@Test("Loading users populates the list")
func loadUsersSucceeds() async throws {
    let mockService = MockUserService()
    mockService.usersToReturn = [User.mock1, User.mock2]
    let sut = UserViewModel(service: mockService)

    await sut.loadUsers()

    // #expect for soft assertions (test continues on failure).
    #expect(sut.users == [User.mock1, User.mock2])
    #expect(sut.isLoading == false)
    #expect(sut.errorMessage == nil)
}

@Test func fetchReturnsUsers() async throws {
    let sut = makeSUT()
    let users = try await sut.fetchUsers()
    // #require unwraps an optional (or checks a condition) and STOPS the test on failure.
    let first = try #require(users.first)
    #expect(!first.name.isEmpty)
}

Suites and setup

// @Suite groups tests; init replaces setUp and each test gets a fresh
// instance (parallel by default, no shared mutable state). For tearDown,
// use deinit — that requires a class or actor suite, not a struct.
@Suite("UserViewModel")
struct UserViewModelTests {
    let sut: UserViewModel
    let mockService: MockUserService

    init() {
        mockService = MockUserService()
        sut = UserViewModel(service: mockService)
    }

    @Test func failureSetsErrorMessage() async {
        mockService.shouldThrowError = true
        await sut.loadUsers()
        #expect(sut.users.isEmpty)
        #expect(sut.errorMessage != nil)
    }
}

Parameterized tests

// One @Test runs once per argument (each shown separately in results).
@Test(arguments: [
    "[email protected]",
    "[email protected]",
    "[email protected]"
])
func validEmails(_ email: String) {
    #expect(Validator.isValidEmail(email))
}

// Expected errors:
@Test func throwsOnBadInput() async throws {
    await #expect(throws: NetworkError.noConnection) {
        try await sut.failingCall()
    }
}

// confirmation replaces XCTestExpectation for callback-based APIs:
@Test func delegateIsNotified() async {
    await confirmation("delegate called") { confirmed in
        sut.onUpdate = { confirmed() }
        await sut.refresh()
    }
}