Vitest is a test framework for JavaScript and TypeScript: a library and command-line tool that runs the automated tests developers write to check their code. It is built on Vite (a build tool and development server for web projects) and is copyrighted by VoidZero Inc. and the Vitest contributors.
A developer installs Vitest as a development dependency and writes test files with expect-style assertions. Because Vitest reuses the project's Vite configuration and plugins, tests transform and resolve code the same way as the app. It works without Vite too, and also for backend code. It is compatible with Jest (an older JavaScript test framework), so expect, snapshot tests, mocks and coverage reports work in a similar way. Watch mode reruns only the tests related to a change. TypeScript, JSX and ES modules work without extra setup, and a browser mode runs component tests in a real browser.
Vitest is free and open source under the MIT license, funded by sponsors.