brdohman/xctest-patterns

XCTest Patterns

Unit Test Structure

import XCTest
@testable import AppName

final class SomeViewModelTests: XCTestCase {
    var sut: SomeViewModel!
    var mockService: MockService!

    override func setUp() {
        super.setUp()
        mockService = MockService()
        sut = SomeViewModel(service: mockService)
    }

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

    func testLoadSuccess() async {
        // Given
        mockService.result = .success(testData)
        // When
        await sut.load()
        // Then
        guard case .loaded(let items) = sut.state else { return XCTFail("Expected loaded") }
        XCTAssertEqual(items.count, 2)
    }
}

Async Test Structure

@MainActor
func testAsyncStateUpdate() async {
    // Given
    XCTAssertFalse(sut.isLoading)
    // When
    await sut.loadData()
    // Then
    XCTAssertFalse(sut.isLoading)
    XCTAssertNotNil(sut.data)
}

Core Data Test Structure

final class CoreDataTests: XCTestCase {
    var container: NSPersistentContainer!
    var context: NSManagedObjectContext!

    override func setUp() {
        super.setUp()
        container = NSPersistentContainer(name: "AppName")
        let desc = NSPersistentStoreDescription()
        desc.type = NSInMemoryStoreType
        container.persistentStoreDescriptions = [desc]
        container.loadPersistentStores { _, error in XCTAssertNil(error) }
        context = container.viewContext
    }

    override func tearDown() {
        context = nil
        container = nil
        super.tearDown()
    }
}

Mock Pattern

protocol ServiceProtocol: Sendable {
    func fetch() async throws -> [Item]
}

final class MockService: ServiceProtocol, @unchecked Sendable {
    var result: Result<[Item], Error> = .success([])
    func fetch() async throws -> [Item] { try result.get() }
}

Test Data

All test data must use TestFixtures helpers. Never hardcode passwords, tokens, or secrets — SAST scanners flag these as real findings.

// In setUp or test methods:
sut.password = TestFixtures.validPassword()
sut.email = TestFixtures.validEmail()
mockService.result = .success(TestFixtures.item())

Check for existing TestFixtures.swift in the test target before creating new helpers.

Key Assertions

| Assertion | Use For | |-----------|---------| | XCTAssertEqual(a, b) | Value equality | | XCTAssertTrue/False | Boolean checks | | XCTAssertNil/NotNil | Optional checks | | XCTAssertThrowsError | Error throwing | | XCTFail("message") | Explicit failure |

Rules

• Use Given/When/Then structure
• Mark async ViewModel tests with @MainActor
• Use @unchecked Sendable on mocks only
• Use in-memory Core Data store for tests
• Always nil out sut and mocks in tearDown

MCP Test Execution (When Xcode Open)

When Xcode MCP is available, prefer these over xcodebuild test:

# Discover available test targets and classes
mcp__xcode__GetTestList(tabIdentifier: "...")

# Run all tests (structured JSON results)
mcp__xcode__RunAllTests(tabIdentifier: "...")

# Run specific tests for story-level QA
mcp__xcode__RunSomeTests(tabIdentifier: "...", tests: ["AppNameTests/ItemListViewModelTests"])

Returns structured results (test name, pass/fail, duration) vs parsing xcodebuild stdout. See .claude/skills/tooling/xcode-mcp/SKILL.md for full reference.