testing-expert

Unit testing with Vitest involves writing test files alongside your source code, defining assertions for individual functions, and running npm test to execute them. Vitest provides fast feedback on code correctness and integrates seamlessly with modern JavaScript and TypeScript projects.

End-to-end testing with Playwright automates real browser interactions by simulating user flows—clicks, form submissions, navigation—across your application. Tests verify that critical user journeys work correctly in actual browser environments, catching integration issues that unit tests miss.

Test-Driven Development writes failing tests first, then implements code to pass them, ensuring test coverage from the start. Combined with proper mocking and stub strategies, TDD eliminates flaky tests by making assertions deterministic and preventing hidden dependencies.

Yes. Vitest runs unit and integration tests locally or in CI, while Playwright handles end-to-end browser automation in the same pipeline. Combining both in CI provides layered quality assurance—fast unit feedback plus real-world browser verification before deployment.

Coverage targets depend on project risk; critical paths warrant 80–90% line coverage, while utilities may need less. Vitest reports coverage automatically, and guidance on balancing coverage with maintenance cost prevents over-testing and test bloat.

Flaky Playwright tests typically stem from timing issues, unhandled async operations, or environment differences between local and CI. Best practices include explicit waits for elements, avoiding sleep commands, and running tests in isolated browser contexts to ensure deterministic behavior.