writing-swift-unit-tests

Deterministic Swift unit tests require observable behavior testing, minimal mocking, single behavioral intent per test, and async cancellation verification. Avoid time-based sleeps and favor Swift Testing over XCTest for new test files.

Prefer Swift Testing for new tests and use XCTest only when extending existing XCTest-based files. Use #expect and #require instead of XCTAssert, and apply descriptive literal test names while avoiding redundant suite annotations.

No, these guidelines explicitly exclude UI tests and snapshot tests. They apply only when adding or modifying unit test files for Swift codebases, focusing on production-quality, behavior-focused unit testing conventions.

#expect and #require are the assertion helpers in Swift Testing that replace XCTAssert. They enforce clearer assertion conventions and align with modern Swift Testing practices for writing maintainable, production-quality unit tests.

Verify async behavior and cancellation directly rather than using time-based sleeps. Ensuring deterministic async behavior requires testing observable outcomes and avoiding implementation coupling in your Swift unit tests.

Minimize mocking whenever possible to reduce implementation coupling and flakiness. Focus on testing observable behavior with single behavioral intent per test to produce maintainable, deterministic Swift unit tests.