vitest

name

vitest

description

Use when the user asks to write, run, or debug tests using Vitest, asks about vitest.config.ts or vite.config.ts test configuration, asks how to mock modules, functions, timers, or globals with the `vi` utility, asks about test coverage setup or thresholds, references Vitest API (describe, it, test, expect, beforeEach, afterAll, etc.), or encounters failing Vitest tests and needs help diagnosing them.

Vitest Skill

Contents

• Quick Start
• When This Skill Activates
• Behavior Guidelines
• References Loading Guide

Quick Start

Minimum setup:

npm install -D vitest

// vitest.config.ts
import { defineConfig } from 'vitest/config'

export default defineConfig({
  test: {
    environment: 'node',
  },
})

First test (src/math.test.ts):

import { describe, it, expect } from 'vitest'
import { add } from './math'

describe('add', () => {
  it('returns the sum of two numbers', () => {
    expect(add(1, 2)).toBe(3)
  })
})

npx vitest        # watch mode
npx vitest run    # single run (CI)

When This Skill Activates

• User asks to write a test for a function, component, or module
• User asks how to configure Vitest or integrate it into an existing Vite project
• User's tests are failing and they need help diagnosing the error
• User asks about mocking, spying, or stubbing in Vitest
• User wants to measure or enforce test coverage

Behavior Guidelines

1. Prefer Vitest-native imports — import describe, it, expect, vi, etc. from 'vitest', not from @jest/* packages.
2. Respect the existing config — read vitest.config.ts or vite.config.ts before suggesting configuration changes.
3. Match the project's test style — check existing test files for naming conventions (*.test.ts vs *.spec.ts, it vs test) and follow them.
4. Use vi for all mocking — never suggest jest.fn(), jest.mock(), etc.
5. Run tests to verify — after writing or modifying tests, suggest running npx vitest run to confirm they pass.

References Loading Guide

Load additional context files based on what the user needs:

Situation	Load
Questions about vitest.config.ts, environments, globals, setupFiles	references/config.md
Questions about describe, it, test, expect, hooks	references/api.md
Questions about vi.fn(), vi.mock(), vi.spyOn(), timers, globals	references/mocking.md
Questions about coverage providers, thresholds, --coverage flag	references/coverage.md

Read only what is relevant to the current question. Do not preload all files unless the user's question spans multiple areas.