Vitest Has a Free API That Makes Unit Testing in Vite Projects Lightning Fast

Vitest is the native test runner for Vite. Same config, same transforms, same plugin ecosystem. Tests run with Vite's speed — instant HMR, native ESM, no Babel.

Quick Start

npm install -D vitest

// vite.config.ts — that's it, Vitest reads your existing Vite config
import { defineConfig } from 'vitest/config'
export default defineConfig({ test: { globals: true } })

Basic Test

import { describe, it, expect } from 'vitest'

describe('math', () => {
  it('adds numbers', () => {
    expect(1 + 1).toBe(2)
  })
})

Jest-Compatible API

import { describe, it, expect, vi, beforeEach } from 'vitest'

// Mocking
const mockFn = vi.fn()
vi.mock('./api', () => ({ fetchData: vi.fn() }))

// Spying
const spy = vi.spyOn(console, 'log')

// Timers
vi.useFakeTimers()
vi.advanceTimersByTime(1000)

Drop-in replacement for Jest. Same describe, it, expect, vi (instead of jest).

Watch Mode (Instant Feedback)

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

Vitest re-runs only affected tests when you save a file — using Vite's module graph.

In-Source Testing

// src/utils.ts
export function add(a: number, b: number) { return a + b }

if (import.meta.vitest) {
  const { it, expect } = import.meta.vitest
  it('adds', () => { expect(add(1, 2)).toBe(3) })
}

Tests live next to the code. Removed from production builds automatically.

Vitest vs Jest

Feature	Vitest	Jest
Config	Vite config	Separate
ESM	Native	Transform
Speed	2-10x faster	Baseline
Watch	Smart (module graph)	Pattern matching
TypeScript	Native	Babel/ts-jest

The Bottom Line

If you use Vite (React, Vue, Svelte, Solid), Vitest is the obvious choice. Same config, faster execution, Jest-compatible API. No reason to use Jest in Vite projects.

---

Need to automate data collection or build custom scrapers? Check out my Apify actors for ready-made tools, or email [e-mail] for custom solutions.