Vitest

Vitest is what happens when someone builds a test runner that actually understands your Vite project. Same config, same transforms, same speed. If you use Vite, switching to Vitest is a no-brainer — your tests run against the same pipeline as your app.

The API is Jest-compatible, so migration is usually find-and-replace on imports. But Vitest is faster because it uses Vite's dev server for transforms instead of Babel. Watch mode is instant. TypeScript works without extra config. Component testing is built in.

Jest is the incumbent — massive ecosystem, works everywhere, but slower and needs more config for modern setups. Testing Library pairs with both. Playwright and Cypress own E2E; Vitest owns unit and integration.

Best for any project using Vite (which is most new projects). Solo founders get fast feedback loops without fighting configuration.

The catch: if you're not on Vite, the advantage shrinks. Jest's ecosystem of custom matchers and reporters is still larger. And some edge cases around ESM/CJS module handling can bite you during migration.