Mocking Berasaskan Protokol dan Suntikan Kebergantungan

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

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 {}
}

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

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

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

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

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

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

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