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Vitest

Anthony FuCommunityCreated by Anthony Fu

  • Skill
  • Tool integration
  • Software development
  • MIT
  • No issues found

From the author

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.
— the description by Anthony Fu

AutoGineer summary

Written by AutoGineer from the skill’s own files, not by the author

Vitest is a testing framework built for the Vite ecosystem. It provides a Jest-compatible API and supports ESM, TypeScript, and JSX by default. It shares configuration, transformers, and plugins with Vite applications, allowing for integrated testing workflows. The framework includes features for mocking, snapshot testing, code coverage, and multi-threaded test execution.

What it does

  • Provides a Jest-compatible API for writing and running unit tests
  • Supports native ESM, TypeScript, and JSX without additional configuration
  • Enables mocking of functions, modules, timers, and dates
  • Offers built-in code coverage reporting using V8 or Istanbul
  • Supports multi-project workspaces and varied test environments like Node, jsdom, and happy-dom
  • Includes utilities for snapshot testing, test filtering, and benchmarking

When to use it

  • When you need a testing framework that integrates directly with your Vite configuration
  • When migrating existing test suites that rely on Jest-compatible APIs
  • When you require specific test environments like jsdom or happy-dom for DOM-related testing
  • When managing complex test setups across monorepos or multiple projects

Advantages

  • Shares configuration and plugins with Vite projects
  • Supports parallel test execution via multi-threaded workers
  • Provides flexible test environment configuration per file or project
  • Includes built-in support for snapshot testing and mocking utilities

Usage examples

“How do I configure Vitest to use the jsdom environment for my tests?”
The agent provides the vitest.config.ts configuration snippet using the environment: 'jsdom' property and explains how to install the necessary jsdom package.
“Can I run different test configurations in the same Vitest process?”
The agent explains how to use the projects field in the vitest.config.ts file to define multiple test suites with different environments or include patterns.

Install

  1. Download the skill as a ZIP:

    https://autogineer.com/agent-skills/antfu/vitest/download
  2. Unzip it into the cross-client skills folder of your project:

    mkdir -p .agents/skills && unzip vitest.zip -d .agents/skills

Documentation by Anthony Fu

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 5.1.0-beta.1, generated at 2026-10-23.

Core

TopicDescriptionReference
ConfigurationVitest and Vite config integration, defineConfig usagecore-config
CLICommand line interface, commands and optionscore-cli
Test APItest/it function, modifiers like skip, only, concurrentcore-test-api
Describe APIdescribe/suite for grouping tests and nested suitescore-describe
Expect APIAssertions with toBe, toEqual, matchers and asymmetric matcherscore-expect
HooksbeforeEach, afterEach, beforeAll, afterAll, aroundEachcore-hooks

Features

TopicDescriptionReference
MockingMock functions, modules, timers, dates with vi utilitiesfeatures-mocking
SnapshotsSnapshot testing with toMatchSnapshot and inline snapshotsfeatures-snapshots
CoverageCode coverage with V8 or Istanbul providersfeatures-coverage
Test ContextTest fixtures, context.expect, test.extend for custom fixturesfeatures-context
ConcurrencyConcurrent tests, parallel execution, shardingfeatures-concurrency
FilteringFilter tests by name, file patterns, tagsfeatures-filtering
Test TagsLabel tests with tags to filter runs and apply shared optionsfeatures-test-tags
ReportersBuilt-in reporters, default selection, CI/output configfeatures-reporters
BenchmarkingWrite benchmarks with the bench fixture (Tinybench)features-benchmarking

Advanced

TopicDescriptionReference
Vi Utilitiesvi helper: mock, spyOn, fake timers, hoisted, waitForadvanced-vi
EnvironmentsTest environments: node, jsdom, happy-dom, customadvanced-environments
Type TestingType-level testing with expectTypeOf and assertTypeadvanced-type-testing
ProjectsMulti-project workspaces, different configs per projectadvanced-projects

Files

references/core-hooks.md


name: lifecycle-hooks description: beforeEach, afterEach, beforeAll, afterAll, and around hooks

Lifecycle Hooks

Basic Hooks

import { afterAll, afterEach, beforeAll, beforeEach, test } from 'vitest'

beforeAll(async () => {
  // Runs once before all tests in file/suite
  await setupDatabase()
})

afterAll(async () => {
  // Runs once after all tests in file/suite
  await teardownDatabase()
})

beforeEach(async () => {
  // Runs before each test
  await clearTestData()
})

afterEach(async () => {
  // Runs after each test
  await cleanupMocks()
})

Cleanup Return Pattern

Return cleanup function from before* hooks:

beforeAll(async () => {
  const server = await startServer()
  
  // Returned function runs as afterAll
  return async () => {
    await server.close()
  }
})

beforeEach(async () => {
  const connection = await connect()
  
  // Runs as afterEach
  return () => connection.close()
})

Scoped Hooks

Hooks apply to current suite and nested suites:

describe('outer', () => {
  beforeEach(() => console.log('outer before'))
  
  test('test 1', () => {}) // outer before → test
  
  describe('inner', () => {
    beforeEach(() => console.log('inner before'))
    
    test('test 2', () => {}) // outer before → inner before → test
  })
})

Hook Timeout

beforeAll(async () => {
  await slowSetup()
}, 30_000) // 30 second timeout

Around Hooks

Wrap tests with setup/teardown context:

import { aroundEach, test } from 'vitest'

// Wrap each test in database transaction
aroundEach(async (runTest) => {
  await db.beginTransaction()
  await runTest() // Must be called!
  await db.rollback()
})

test('insert user', async () => {
  await db.insert({ name: 'Alice' })
  // Automatically rolled back after test
})
aroundAll

Wrap entire suite:

import { aroundAll, test } from 'vitest'

aroundAll(async (runSuite) => {
  console.log('before all tests')
  await runSuite() // Must be called!
  console.log('after all tests')
})
Multiple Around Hooks

Nested like onion layers:

aroundEach(async (runTest) => {
  console.log('outer before')
  await runTest()
  console.log('outer after')
})

aroundEach(async (runTest) => {
  console.log('inner before')
  await runTest()
  console.log('inner after')
})

// Order: outer before → inner before → test → inner after → outer after

Test Hooks

Inside test body:

import { onTestFailed, onTestFinished, test } from 'vitest'

test('with cleanup', () => {
  const db = connect()
  
  // Runs after test finishes (pass or fail)
  onTestFinished(() => db.close())
  
  // Only runs if test fails
  onTestFailed(({ task }) => {
    console.log('Failed:', task.result?.errors)
  })
  
  db.query('SELECT * FROM users')
})
Reusable Cleanup Pattern
function useTestDb() {
  const db = connect()
  onTestFinished(() => db.close())
  return db
}

test('query users', () => {
  const db = useTestDb()
  expect(db.query('SELECT * FROM users')).toBeDefined()
})

test('query orders', () => {
  const db = useTestDb() // Fresh connection, auto-closed
  expect(db.query('SELECT * FROM orders')).toBeDefined()
})

Concurrent Test Hooks

For concurrent tests, use context's hooks:

test.concurrent('concurrent', ({ onTestFinished }) => {
  const resource = allocate()
  onTestFinished(() => resource.release())
})

Extended Test Hooks

With test.extend, hooks are type-aware and must be called on the extended test:

const test = base
  .extend('db', { scope: 'file' }, async ({}, { onCleanup }) => {
    const db = await createDb()
    onCleanup(() => db.close())
    return db
  })

// Test-level hooks see fixtures
test.beforeEach(({ db }) => db.seed())
test.afterEach(({ db }) => db.clear())

// Suite-level hooks (4.1+) can access file/worker-scoped fixtures
test.beforeAll(({ db }) => db.createUsers())
test.aroundAll(async (runSuite, { db }) => db.transaction(runSuite))

Suite-level hooks (beforeAll/afterAll/aroundAll) only see file/worker-scoped fixtures, and the global beforeAll/afterAll cannot access custom fixtures — use test.beforeAll etc.

Hook Execution Order

Default order (stack):

  1. beforeAll (in order)

  2. beforeEach (in order)

  3. Test

  4. afterEach (reverse order)

  5. afterAll (reverse order)

Configure with sequence.hooks:

defineConfig({
  test: {
    sequence: {
      hooks: 'list', // 'stack' (default), 'list', 'parallel'
    },
  },
})

Key Points

  • Hooks are not called during type checking

  • Return cleanup function from before* to avoid after* duplication

  • aroundEach/aroundAll must call runTest()/runSuite()

  • onTestFinished always runs, even if test fails

  • Use context hooks for concurrent tests

<!-- Source references: - https://vitest.dev/api/hooks.html -->

Requirements and compatibility

Works with: Claude Code, Claude apps, OpenAI Codex, GitHub Copilot, Cursor, Gemini CLI, Kiro, OpenCode, Goose, Amp, Roo Code, JetBrains Junie, Factory Droid, Devin (ex-Windsurf), Mistral Vibe, OpenHands, Letta

“Works with” means the tool reads the open Agent Skills format; a skill written for one tool may use features others lack.

Needs: Needs Node.js

Security

No issues found by our static scan· No issues found

A static scan is not a guarantee. Skills are third-party content: review a skill before you let an agent use it.

Attribution and licence

Created by
Anthony Fu
Publisher
Anthony Fu (Community)
Source
antfu/skills · skills/vitest · commit f63e9ec
Licence
MIT License (redistribution allowed)
  • LICENSE (added by AutoGineer from LICENSE.md)
  • ATTRIBUTION.md (written by AutoGineer)
Synced

AutoGineer is not affiliated with or endorsed by Anthony Fu or Anthony Fu.

Download ZIP

The ZIP holds the skill’s files, its licence files and an ATTRIBUTION.md. Download vitest.zip