Swift Testing

Covers the modern Swift Testing framework that ships with Xcode 16 and Swift 6. You'll reach for this when migrating from XCTest or writing new unit tests with @Test macros, #expect assertions, and parameterized tests. The skill is opinionated about execution model details that trip people up, like parallel test execution by default and when to actually use .serialized. It includes practical patterns for async testing with confirmation counts, withKnownIssue for flaky tests, and a solid common mistakes section that calls out things like using sleep instead of confirmation. The review checklist alone makes it worth having around when you're setting up a new test suite.