What tests do you need?
|
+-- Unit tests for business logic
|   +-- Swift Testing (@Test, #expect) -- recommended for iOS 16+
|   +-- XCTest -- for iOS 13-15 support or existing XCTest projects
|
+-- Integration tests (component interactions)
|   +-- Protocol-based mocks with dependency injection
|
+-- UI tests
|   +-- XCUITest with Screen Object pattern
|
+-- Snapshot/preview tests
    +-- PreviewSnapshots or swift-snapshot-testing

Glob: **/*Tests.swift, **/*Tests/**/*.swift, **/*Spec.swift
Grep: "import XCTest" or "import Testing" or "@Suite" or "@Test"
Grep: "MockItemRepository" or "protocol.*Repository" or "class Mock"

Grep: "ViewModel" or "Reducer" or "UseCase" or "Repository" or "Service"
Glob: **/*ViewModel.swift, **/*Reducer.swift, **/*Repository.swift

Tests/UnitTests/
├── ViewModelTests/
│   └── ItemViewModelTests.swift
├── ServiceTests/
│   └── APIClientTests.swift
└── RepositoryTests/
    └── ItemRepositoryTests.swift

Tests/UITests/
├── Screens/
│   └── HomeScreenTests.swift
├── Flows/
│   └── OnboardingFlowTests.swift
└── Helpers/
    └── TestHelpers.swift

import Testing
@testable import YourApp

@Suite("Item ViewModel Tests")
struct ItemViewModelTests {

    @Test("loads items successfully")
    func loadsItems() async throws {
        let mockRepository = MockItemRepository()
        let viewModel = ItemViewModel(repository: mockRepository)

        await viewModel.loadItems()

        #expect(viewModel.items.count == 3)
        #expect(viewModel.isLoading == false)
    }

    @Test("handles empty state")
    func handlesEmptyState() async {
        let mockRepository = MockItemRepository(items: [])
        let viewModel = ItemViewModel(repository: mockRepository)

        await viewModel.loadItems()

        #expect(viewModel.items.isEmpty)
        #expect(viewModel.showEmptyState)
    }
}

@Test("validates email format", arguments: [
    ("valid@email.com", true),
    ("invalid", false),
    ("no@tld", false),
    ("test@domain.co.uk", true)
])
func validatesEmail(email: String, isValid: Bool) {
    #expect(EmailValidator.isValid(email) == isValid)
}

import XCTest
@testable import YourApp

final class ItemViewModelTests: XCTestCase {

    var sut: ItemViewModel!
    var mockRepository: MockItemRepository!

    override func setUp() {
        super.setUp()
        mockRepository = MockItemRepository()
        sut = ItemViewModel(repository: mockRepository)
    }

    override func tearDown() {
        sut = nil
        mockRepository = nil
        super.tearDown()
    }

    func testLoadsItems() async throws {
        await sut.loadItems()

        XCTAssertEqual(sut.items.count, 3)
        XCTAssertFalse(sut.isLoading)
    }
}

@Suite("ViewModel Tests")
struct ViewModelTests {

    @Test("state transitions correctly")
    func stateTransitions() async {
        let vm = ItemViewModel(repository: MockItemRepository())

        #expect(vm.state == .idle)

        await vm.loadItems()

        #expect(vm.state == .loaded)
    }

    @Test("error handling")
    func errorHandling() async {
        let failingRepo = MockItemRepository(shouldFail: true)
        let vm = ItemViewModel(repository: failingRepo)

        await vm.loadItems()

        #expect(vm.state == .error)
        #expect(vm.errorMessage != nil)
    }
}

@Test("fetches data asynchronously")
func fetchesData() async throws {
    let service = APIService()

    let result = try await service.fetchItems()

    #expect(result.count > 0)
}

@Test("times out appropriately")
func timesOut() async {
    await #expect(throws: TimeoutError.self) {
        try await withTimeout(seconds: 1) {
            try await Task.sleep(for: .seconds(5))
        }
    }
}

protocol ItemRepository {
    func fetchItems() async throws -> [Item]
    func saveItem(_ item: Item) async throws
}

final class MockItemRepository: ItemRepository {
    var items: [Item] = []
    var shouldFail = false
    var saveCallCount = 0

    func fetchItems() async throws -> [Item] {
        if shouldFail {
            throw TestError.mockFailure
        }
        return items
    }

    func saveItem(_ item: Item) async throws {
        saveCallCount += 1
        items.append(item)
    }
}

import XCTest

final class HomeScreen {
    let app: XCUIApplication

    init(app: XCUIApplication) {
        self.app = app
    }

    var itemList: XCUIElement {
        app.collectionViews["itemList"]
    }

    var addButton: XCUIElement {
        app.buttons["addItem"]
    }

    func tapItem(at index: Int) {
        itemList.cells.element(boundBy: index).tap()
    }

    func addNewItem(title: String) {
        addButton.tap()
        app.textFields["itemTitle"].tap()
        app.textFields["itemTitle"].typeText(title)
        app.buttons["save"].tap()
    }
}

# Command line
xcodebuild test -scheme YourApp -destination 'platform=iOS Simulator,name=iPhone 16'

# With coverage
xcodebuild test -scheme YourApp -enableCodeCoverage YES