swift-testing-expert

Migrate incrementally: convert XCTAssert calls to #expect, replace XCTUnwrap with try #require, and turn test methods into @Test functions. XCTest and Swift Testing can coexist in the same target, so convert assertions first, then reorganize suites, then add parameterization and traits.

Pass a sendable collection to @Test(arguments:) so each element becomes an independent test case. For paired inputs, prefer arrays of tuples or dictionaries over zip, since zip silently truncates mismatched lengths and breaks if CaseIterable ordering changes.

Use try #require when later assertions depend on a prerequisite value, such as unwrapping an optional. It fails the test early and returns the unwrapped value, while #expect records a failure and lets the test continue.

Swift Testing runs tests in parallel with randomized order, which exposes shared mutable state like globals and singletons. Fix flakiness by isolating state per test or using in-memory dependencies; apply .serialized only as a temporary transition measure.

Yes, both frameworks coexist in one target and even one file can import both XCTest and Testing. Keep XCTest for UI automation with XCUIApplication, performance metrics with XCTMetric, and Objective-C-only tests, since Swift Testing does not cover those.

Bridge completion handlers with withCheckedContinuation or withCheckedThrowingContinuation so the test can await the result. For event-style callbacks that are not naturally awaitable, use confirmations with an explicit expected count instead of sleeps.