swift-testing-expert

Migrate incrementally: convert XCTAssert assertions to #expect first, then replace test class methods with @Test functions, then add parameterization and traits. Swift Testing and XCTest can coexist in the same target, so you never need a full rewrite at once.

Use try #require when later assertions depend on a prerequisite value, such as unwrapping an optional before testing its properties. It acts as a guard that fails the test early, while #expect is the default for ordinary assertions.

Yes. Keep XCTest for UI automation with XCUIApplication, performance metrics with XCTMetric, and Objective-C-only test code, since Swift Testing does not cover those scenarios. Everything else can migrate to Swift Testing.

Flakiness usually comes from shared mutable state, hidden ordering dependencies, or time-based waits, because Swift Testing runs tests in parallel with randomized order. Isolate state per test, use in-memory dependencies, and apply .serialized only as a temporary transition measure.

Bridge completion-handler APIs using withCheckedContinuation or withCheckedThrowingContinuation so tests can await results naturally. For event-style callbacks that are not awaitable, use confirmations with explicit expected counts instead of sleeps.

zip silently truncates to the shorter collection and breaks if CaseIterable enum cases are reordered, causing missing coverage without any error. Prefer arrays of tuples or dictionaries for paired inputs so each case and its expected value stay co-located.