swift-testing

# Swift Testing Patterns ## XCTest Basics XCTest is Apple's foundational testing framework. Every test class inherits from `XCTestCase` and uses `setUp`/`tearDown` for lifecycle management. ```swift import XCTest @testable import MyApp final class UserServiceTests: XCTestCase { var sut: UserService! var mockStore: MockUserStore! override func setUp() { super.setUp() mockStore = MockUserStore() sut = UserService(store: mockStore) } override func tearDown() { sut = nil mockStore = nil super.tearDown() } func testFetchUser_withValidID_returnsUser() { mockStore.stubbedUser = User(id: "1", name: "Alice") let user = sut.fetchUser(id: "1") XCTAssertNotNil(user) XCTAssertEqual(user?.name, "Alice") } func testFetchUser_withInvalidID_returnsNil() { mockStore.stubbedUser = nil let user = sut.fetchUser(id: "unknown") XCTAssertNil(user) } } ``` ## Swift Testing Framework (Swift 5.9+) The Swift Testing framework replaces XCTest with a more expressive, macro-driven approach. Use `@Test` for individual tests, `#expect` for assertions, and `@Suite` for grouping. ```swift import Testing @testable import MyApp @Suite("User Service") struct UserServiceTests { let mockStore = MockUserStore() @Test("fetches user by valid ID") func fetchValidUser() { mockStore.stubbedUser = User(id: "1", name: "Alice") let servic...