Tests Developer Skill

XCTest is Swift's built-in testing framework. Create test files ending in Tests.swift, organize them by category, and use XCTest assertions like XCTAssertEqual to verify behavior. This Skill provides patterns for structuring tests, applying edge-case coverage, and maintaining consistency across your project.

Swift Testing is a newer framework offering a more flexible API with the #expect macro, while XCTest is the established standard. This Skill covers both frameworks, helping you choose based on your project needs and apply the appropriate assertion styles and test organization for each.

Mocks replace real dependencies during testing to isolate code behavior. Dependency injection passes mock objects into your code instead of creating them internally. This Skill guides you through creating mock helpers, structuring tests for testability, and keeping mocks synchronized with refactors.

Consistent file naming and folder structure keep tests maintainable. This Skill implements conventions like AnyTypeTests/[Category]/[TestFile]Tests.swift, establishes annotation standards, and ensures test organization scales across your codebase.

Test-driven development writes tests before implementation to guide design. This Skill supports TDD workflows by providing patterns for creating production test scaffolds, organizing tests by feature, and maintaining alignment between tests and code changes throughout development.

Edge cases are boundary conditions, null values, empty collections, and error states that expose bugs. This Skill emphasizes systematic edge-case coverage, test organization by scenario, and assertion practices that catch subtle failures without over-testing.