vitest-v4

Unit tests for TypeScript React components use Vitest v4 with jsdom environment enabled in vitest.config.ts. Write test files colocated with source, import components and testing utilities, then run tests with `nlx vitest run`. Vitest handles TypeScript types and path aliases automatically when configured.

Yes, Vitest v4 works with Next.js projects when configured with jsdom environment and proper path aliases in vitest.config.ts. This setup supports both unit and component testing across TypeScript-based Next.js applications in a browser-like environment.

Organize tests by collocating test files with source code and use dedicated mock and utility directories for shared test setup. Vitest v4 provides mocking utilities to isolate components and functions, enabling reliable unit and component test patterns across your TypeScript codebase.

Debug failing Vitest tests by running watch mode with `nlx vitest`, using pattern-based test selection with `-t "pattern"`, and running specific test files directly. jsdom environment mimics browser behavior, so failures often relate to DOM queries or React component lifecycle.

Yes, Vitest requires a vitest.config.ts file configured with jsdom environment, TypeScript support, and path aliases matching your project setup. Once configured, run tests immediately with `nlx vitest run` or enable watch mode with `nlx vitest`.

Vitest v4 runs React component tests in jsdom, a browser-like JavaScript environment that simulates DOM APIs. This allows testing React components as users interact with them, rather than testing in Node.js, and integrates seamlessly with TypeScript type checking.