Dart Matcher Best Practices

This one helps you write cleaner test assertions in Dart by moving from manual checks to proper matchers from package:matcher. It shows you how to replace things like expect(list.length, 3) with expect(list, hasLength(3)), or manual map lookups with containsPair. The regex patterns are handy for finding code to improve in your codebase. The having() examples for chaining property checks are solid, and the async section clears up a common gotcha with expectLater timing. If you've got tests that feel clunky or produce confusing failure messages, this gives you the patterns to fix them.