Modern TypeScript/JavaScript testing with Vitest. Fast unit and integration tests, native ESM support, Vite-powered HMR, and comprehensive mocking. Use for testing TS/JS projects.
/plugin marketplace add secondsky/claude-skills/plugin install vitest-testing@claude-skillsThis skill is limited to using the following tools:
Expert knowledge for testing JavaScript/TypeScript projects using Vitest - a blazingly fast testing framework powered by Vite.
# Using Bun (recommended)
bun add -d vitest
# Using npm
npm install -D vitest
// vitest.config.ts
import { defineConfig } from 'vitest/config'
export default defineConfig({
test: {
globals: true,
environment: 'node', // or 'jsdom'
coverage: {
provider: 'v8',
reporter: ['text', 'json', 'html'],
thresholds: { lines: 80, functions: 80, branches: 80 },
},
include: ['**/*.{test,spec}.{js,ts,jsx,tsx}'],
},
})
# Run all tests (prefer bun)
bun test
# Watch mode (default)
bun test --watch
# Run once (CI mode)
bun test --run
# With coverage
bun test --coverage
# Specific file
bun test src/utils/math.test.ts
# Pattern matching
bun test --grep="calculates sum"
# UI mode (interactive)
bun test --ui
# Verbose output
bun test --reporter=verbose
import { describe, it, expect, beforeEach, afterEach } from 'vitest'
import { add, subtract } from './math'
describe('Math utilities', () => {
beforeEach(() => {
// Setup before each test
})
it('adds two numbers correctly', () => {
expect(add(2, 3)).toBe(5)
})
it('subtracts two numbers correctly', () => {
expect(subtract(5, 3)).toBe(2)
})
})
describe.each([
{ input: 2, expected: 4 },
{ input: 3, expected: 9 },
])('square function', ({ input, expected }) => {
it(`squares ${input} to ${expected}`, () => {
expect(square(input)).toBe(expected)
})
})
// Equality
expect(value).toBe(expected)
expect(value).toEqual(expected)
// Truthiness
expect(value).toBeTruthy()
expect(value).toBeNull()
expect(value).toBeDefined()
// Numbers
expect(number).toBeGreaterThan(3)
expect(number).toBeCloseTo(0.3, 1)
// Strings/Arrays
expect(string).toMatch(/pattern/)
expect(array).toContain(item)
// Objects
expect(object).toHaveProperty('key')
expect(object).toMatchObject({ a: 1 })
// Exceptions
expect(() => throwError()).toThrow('message')
// Promises
await expect(promise).resolves.toBe(value)
await expect(promise).rejects.toThrow()
import { vi } from 'vitest'
const mockFn = vi.fn()
mockFn.mockReturnValue(42)
mockFn.mockResolvedValue('async result')
mockFn.mockImplementation((x) => x * 2)
expect(mockFn).toHaveBeenCalled()
expect(mockFn).toHaveBeenCalledWith('arg')
vi.mock('./api', () => ({
fetchUser: vi.fn(() => ({ id: 1, name: 'Test User' })),
}))
import { fetchUser } from './api'
beforeEach(() => {
vi.clearAllMocks()
})
beforeEach(() => vi.useFakeTimers())
afterEach(() => vi.restoreAllMocks())
it('advances timers', () => {
const callback = vi.fn()
setTimeout(callback, 1000)
vi.advanceTimersByTime(1000)
expect(callback).toHaveBeenCalledOnce()
})
it('mocks dates', () => {
const date = new Date('2024-01-01')
vi.setSystemTime(date)
expect(Date.now()).toBe(date.getTime())
})
# Generate coverage report
bun test --coverage
# HTML report
bun test --coverage --coverage.reporter=html
open coverage/index.html
# Check against thresholds
bun test --coverage --coverage.thresholds.lines=90
import request from 'supertest'
import { app } from './app'
describe('API endpoints', () => {
it('creates a user', async () => {
const response = await request(app)
.post('/api/users')
.send({ name: 'John' })
.expect(201)
expect(response.body).toMatchObject({
id: expect.any(Number),
name: 'John',
})
})
})
math.ts → math.test.tsdescribe() blocksconcurrent tests for independent async testsbeforeAll()test-quality-analysis - Detecting test smellsplaywright-testing - E2E testingmutation-testing - Validate test effectivenessMaster authentication and authorization patterns including JWT, OAuth2, session management, and RBAC to build secure, scalable access control systems. Use when implementing auth systems, securing APIs, or debugging security issues.