vitest

Vite-powered unit testing framework with Jest-compatible API and native ESM support.

- Shares Vite's config, transformers, and plugins; supports TypeScript, JSX, and ESM without extra setup

- Smart watch mode reruns only affected tests based on module graph; multi-threaded workers enable parallel execution

- Comprehensive testing utilities: test/describe/expect API, mocking (functions, modules, timers), snapshots, and fixtures

- Built-in code coverage via V8 or Istanbul; test filtering by name, file patterns, and tags

- Advanced features include type-level testing, custom environments (node, jsdom, happy-dom), and multi-project workspaces

Vitest is a next-generation testing framework powered by Vite. It provides a Jest-compatible API with native ESM, TypeScript, and JSX support out of the box. Vitest shares the same config, transformers, resolvers, and plugins with your Vite app.

Key Features:

- Vite-native: Uses Vite's transformation pipeline for fast HMR-like test updates

- Jest-compatible: Drop-in replacement for most Jest test suites

- Smart watch mode: Only reruns affected tests based on module graph

- Native ESM, TypeScript, JSX support without configuration

- Multi-threaded workers for parallel test execution

- Built-in coverage via V8 or Istanbul

- Snapshot testing, mocking, and spy utilities

The skill is based on Vitest 3.x, generated at 2026-01-28.

Core