Vitest

Vitest is a test runner that shares Vite's config and transform pipeline. If your project uses Vite, Vitest works with zero additional configuration — same TypeScript handling, same path aliases, same module resolution.

The watch mode is instant. HMR-based re-running means only affected tests run on file changes. Jest-compatible API means migration is straightforward — rename the imports and most tests work unchanged. Combined with Testing Library for component tests, it's the complete replacement for the Jest ecosystem.