Vitest — Blazing Fast Unit Testing

Overview

Vitest is the Vite-native testing framework. It runs unit, integration and component tests with native TypeScript support, a Jest-compatible API, built-in mocking, code coverage, snapshot testing and watch mode — reusing Vite's transform pipeline, so tests need no separate compilation step. This skill targets Vitest 5 (released September 2026), which changed several defaults; the Guidelines list what to check when upgrading.

Instructions

Installation

npm install -D vitest
npm install -D @vitest/coverage-v8         # Coverage
npm install -D @vitest/ui                  # Browser UI
npm install -D jsdom                       # Only for environment: "jsdom"

Vitest 5 needs Node.js 22.12+ and Vite 6.4+. Vite is a peer dependency: npm, pnpm and Bun install it automatically, Yarn needs yarn add -D vitest vite. Add .vitest/ (reports and artifacts) and coverage/ to .gitignore.