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vitest Vitest fast unit testing framework powered by Vite with Jest-compatible API. Use when writing tests, mocking, configuring coverage, or working with test filtering and fixtures.
author version source
Anthony Fu 2026.1.28 Generated from https://github.com/vitest-dev/vitest, scripts located at https://github.com/antfu/skills

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

Topic Description Reference
Configuration Vitest and Vite config integration, defineConfig usage core-config
CLI Command line interface, commands and options core-cli
Test API test/it function, modifiers like skip, only, concurrent core-test-api
Describe API describe/suite for grouping tests and nested suites core-describe
Expect API Assertions with toBe, toEqual, matchers and asymmetric matchers core-expect
Hooks beforeEach, afterEach, beforeAll, afterAll, aroundEach core-hooks

Features

Topic Description Reference
Mocking Mock functions, modules, timers, dates with vi utilities features-mocking
Snapshots Snapshot testing with toMatchSnapshot and inline snapshots features-snapshots
Coverage Code coverage with V8 or Istanbul providers features-coverage
Test Context Test fixtures, context.expect, test.extend for custom fixtures features-context
Concurrency Concurrent tests, parallel execution, sharding features-concurrency
Filtering Filter tests by name, file patterns, tags features-filtering

Advanced

Topic Description Reference
Vi Utilities vi helper: mock, spyOn, fake timers, hoisted, waitFor advanced-vi
Environments Test environments: node, jsdom, happy-dom, custom advanced-environments
Type Testing Type-level testing with expectTypeOf and assertType advanced-type-testing
Projects Multi-project workspaces, different configs per project advanced-projects