Testing and validation

Add a colocated .test.tsx file for new components and changed behavior.
Use Vitest and Testing Library to test behavior visible to users. Prefer accessible queries and user interactions over implementation details.
Cover relevant loading, error, empty, and success states as well as important interactions.
Do not test React, Chakra UI, React Router, or other third-party internals.
Keep tests deterministic and restore mocks between tests.
Before finishing a change, run pnpm lint, pnpm test, and pnpm build. Run pnpm format when source formatting changes.