Testing

This teaches you to write tests the way users actually interact with your app, not by poking at internal state. It's built around React Testing Library and Vitest, with a clear hierarchy: use getByRole first, getByLabelText for forms, and only reach for getByTestId when nothing else works. The guide hammers on userEvent over fireEvent, waiting with findBy instead of arbitrary timeouts, and keeping toBeInTheDocument even though getBy already throws, because it signals intent to whoever reads your test later. Includes MSW setup templates and a solid list of mistakes people actually make, like querying with container.querySelector or wrapping everything in act.