Swift Testing Standards skill

Swift Testing Standards

Priority: P0 (CRITICAL)

Core Rule Anchors

• [MOB-TEST-01] Tripartite Naming: Test functions must follow test_method_scenario_expectedBehavior or testMethod_scenario_expectedBehavior.
• [MOB-TEST-02] State Invariant Rule: Assert state transitions and invariants; ban trivial state mirror tests.
• [MOB-TEST-03] Entity Invariant & Codable Rule: Test calculations, validations, domain invariants, and non-trivial Codable serialization/parsing or error mapping; ban testing trivial getters or echo tests.
• [MOB-TEST-04] Contract Testing Rule: Repositories and data sources must be tested for contract compliance and error mapping; ban 1:1 pass-through mock echoing.
• [MOB-TEST-05] Bug-First Regression Lock: Every PR fixing a bug ticket or with title fix(...) must introduce a test reproducing the defect prior to the fix.

Write XCTest Cases

• Standard Naming: Test functions must prefixed by 'test' ([MOB-TEST-01], e.g., func test_userLogin_whenValid_isSuccessful()).
• Setup/Teardown: Use setUpWithError() and tearDownWithError() for environment management.
• Assertions: Use specific assertions: XCTAssertEqual, XCTAssertNil, XCTAssertTrue, etc.

See implementation examples for XCTest setup/teardown, async tests, and UI test patterns.

Test Async Code

• Async/Await: Mark test methods as async throws and use try await directly inside them.
• Expectations: Use XCTestExpectation for callback-based async logic. Call expectation then fulfill() when done; then wait(for: [exp], timeout: 2.0) to block.
• Timeout: Always set reasonable timeouts for expectations to avoid hanging CI.

Organize Test Suites

• Unit Tests: Use protocols for dependencies and inject them via constructor (e.g., init(service: ServiceProtocol)). Focus on logic isolation using mocks/stubs.
• UI Tests: Test user flows using XCUIApplication and accessibility identifiers.
• Coverage: Coverage is diagnostic and project-configured; verify risk-weighted critical paths rather than padding code for an arbitrary percentage.

Anti-Patterns

• [MOB-TEST-01..05] Violations: Ban vague names, trivial state mirrors, echo tests, 1:1 mock echoing, and unverified bug fixes.
• No Thread.sleep: Use expectations or await.
• No force unwrap in tests: Use XCTUnwrap() for better failure messages.
• No assertion-free tests: A test that only runs code without asserting contract invariants is not a test.

References

• XCTest Patterns & Async Tests

Canonical response anchors

When this skill applies, preserve the following domain terminology or equivalent concrete examples in the answer when relevant:

• Inject them via constructor
• Use protocols
• prefixed by 'test'