Mocking Berbasis Protokol dan Injeksi Dependensi

Mengapa Mocking Berbasis Protokol?

protocol NetworkService {
  func fetch(url: URL) async throws -> Data
}
class RealNetworkService: NetworkService { /* URLSession */ }
class MockNetworkService: NetworkService { /* returns fixtures */ }

Mendefinisikan Protokol

protocol UserRepository {
  func getUser(id: Int) async throws -> User
  func saveUser(_ user: User) async throws
}

Injeksi melalui Inisialisator

class ProfileViewModel {
  private let repo: UserRepository
  init(repo: UserRepository = RealUserRepository()) {
    self.repo = repo
  }
}

Menulis Mock

class MockUserRepo: UserRepository {
  var fetchedIds: [Int] = []
  var stubbedUser: User = User(id: 1, name: "Test")
  func getUser(id: Int) async throws -> User {
    fetchedIds.append(id)
    return stubbedUser
  }
  func saveUser(_ user: User) async throws {}
}

Nilai Kembalian Stub

let mock = MockUserRepo()
mock.stubbedUser = User(id: 42, name: "Alice")
let vm = ProfileViewModel(repo: mock)
await vm.loadProfile(id: 42)
XCTAssertEqual(vm.userName, "Alice")

Memverifikasi Interaksi

XCTAssertEqual(mock.fetchedIds, [42], "Should fetch user 42 exactly once")

Simulasi Kesalahan

class FailingRepo: UserRepository {
  func getUser(id: Int) async throws -> User { throw NetworkError.notFound }
  func saveUser(_ user: User) async throws { throw NetworkError.serverError(500) }
}

Injeksi Properti

class OrderService {
  var paymentGateway: PaymentGateway = StripeGateway()
}
let service = OrderService()
service.paymentGateway = MockPaymentGateway()

Injeksi @Environment / @EnvironmentObject

let mockStore = MockCartStore()
let view = CartView().environmentObject(mockStore)

Menghindari Mocking Berlebihan

// OK to use real DateFormatter in tests — it's deterministic
// Mock URLSession — network I/O is slow and non-deterministic

Komposisi Protokol untuk Antarmuka yang Lebih Sempit

protocol Readable { func read() async throws -> [Item] }
protocol Writable { func write(_ item: Item) async throws }
typealias ReadWrite = Readable & Writable

Pemeriksaan Singkat

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