Jest

Jest was the default JavaScript test runner for years. It works, but the configuration complexity, slow startup, and custom module resolution create friction that Vitest eliminates entirely.

Vitest shares your Vite config — same transforms, same path aliases, same module resolution. Zero additional setup. The watch mode uses HMR for near-instant re-runs. The API is Jest-compatible, so migration is a find-and-replace on imports. There's no reason to start new projects with Jest when Vitest exists.