Unit Test vs Integration Test Comparison

// Swift - Unit test examples (XCTest + Swift Testing)
import Testing
import Foundation
@testable import MyApp

// Swift Testing framework (iOS 17+, WWDC 2024)
struct PriceFormatterTests {

    @Test("Turkish lira formatting should be correct")
    func turkishLiraFormat() {
        let formatter = PriceFormatter(locale: Locale(identifier: "tr_TR"))
        #expect(formatter.format(1234.5) == "₺1.234,50")
        #expect(formatter.format(0) == "₺0,00")
        #expect(formatter.format(-50) == "-₺50,00")
    }

    @Test("Invalid price should not be negative",
          arguments: [-1.0, -100.0, -0.01])
    func negativePriceValidation(price: Double) {
        let validator = PriceValidator()
        #expect(!validator.isValid(price))
    }
}

struct CartViewModelTests {
    var sut: CartViewModel!
    var mockRepository: MockCartRepository!

    @Test("Total price should update when a product is added")
    mutating func addProductUpdatesTotalPrice() async throws {
        mockRepository = MockCartRepository()
        sut = CartViewModel(repository: mockRepository)

        let product = Product(id: "p1", name: "MacBook", price: 75000)
        await sut.addProduct(product)

        #expect(sut.totalPrice == 75000)
        #expect(sut.itemCount == 1)
    }

    @Test("Quantity should increase when the same product is added twice")
    mutating func addSameProductIncreasesQuantity() async throws {
        mockRepository = MockCartRepository()
        sut = CartViewModel(repository: mockRepository)

        let product = Product(id: "p1", name: "MacBook", price: 75000)
        await sut.addProduct(product)
        await sut.addProduct(product)

        #expect(sut.items.count == 1)
        #expect(sut.items.first?.quantity == 2)
        #expect(sut.totalPrice == 150000)
    }
}

// Mock implementation
class MockCartRepository: CartRepositoryProtocol {
    var savedItems: [CartItem] = []

    func save(_ item: CartItem) async throws {
        savedItems.append(item)
    }

    func fetchAll() async throws -> [CartItem] {
        return savedItems
    }
}

// Swift - Integration test examples
import XCTest
@testable import MyApp

// Integration test with in-memory SQLite
class UserRepositoryIntegrationTests: XCTestCase {
    var repository: UserRepository!
    var database: TestDatabase!

    override func setUp() async throws {
        // We use a real in-memory SQLite database
        database = try await TestDatabase.inMemory()
        repository = UserRepository(database: database)
    }

    override func tearDown() async throws {
        try await database.cleanup()
        database = nil
        repository = nil
    }

    func testCreateAndFetchUser() async throws {
        // Create
        let userId = try await repository.createUser(
            name: "Ahmet Yilmaz",
            email: "[email protected]"
        )

        // Fetch
        let fetchedUser = try await repository.fetchUser(id: userId)

        XCTAssertNotNil(fetchedUser)
        XCTAssertEqual(fetchedUser?.name, "Ahmet Yilmaz")
        XCTAssertEqual(fetchedUser?.email, "[email protected]")
    }

    func testDeleteUserCascadesToPosts() async throws {
        let userId = try await repository.createUser(name: "Test", email: "[email protected]")
        let postRepo = PostRepository(database: database)
        _ = try await postRepo.createPost(title: "Post 1", userId: userId)
        _ = try await postRepo.createPost(title: "Post 2", userId: userId)

        // Delete the user
        try await repository.deleteUser(id: userId)

        // The user's posts should be deleted too (cascade)
        let posts = try await postRepo.fetchPosts(userId: userId)
        XCTAssertTrue(posts.isEmpty, "Deleting the user should also delete their posts")
    }
}

// Network integration test with a real URLSession
class APIClientIntegrationTests: XCTestCase {
    func testFetchPublicAPIData() async throws {
        // This test uses a real network connection
        // Should only run in CI environments with network access
        try XCTSkipUnless(ProcessInfo.processInfo.environment["INTEGRATION_TESTS"] == "1")

        let client = APIClient(baseURL: URL(string: "https://jsonplaceholder.typicode.com")!)
        let posts: [Post] = try await client.request(path: "/posts")
        XCTAssertFalse(posts.isEmpty)
        XCTAssertEqual(posts.count, 100)
    }
}