Vitest Has a Free Test Runner — Jest but 10x Faster With Native ESM

Jest Is Showing Its Age

Jest was the gold standard for JavaScript testing. But in 2026, it struggles with ESM imports, needs Babel transforms, and runs slowly on large projects.

Vitest: Vite-Powered Testing

Vitest is a test runner powered by Vite. It reuses your Vite config, understands ESM natively, and runs tests blazingly fast.

Speed Comparison

Jest (500 tests): 12 seconds
Vitest (500 tests): 1.5 seconds

8x faster. On watch mode, tests re-run in milliseconds because Vitest only transforms changed files.

Jest-Compatible API

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

describe('Calculator', () => {
  it('adds numbers', () => {
    expect(add(2, 3)).toBe(5)
  })

  it('mocks functions', () => {
    const fn = vi.fn().mockReturnValue(42)
    expect(fn()).toBe(42)
    expect(fn).toHaveBeenCalledOnce()
  })
})

Same API as Jest. vi.fn() instead of jest.fn(). That is the only change for most tests.

Why Developers Switch

1. Native ESM Support

// This just works. No Babel. No transforms.
import { fetchUser } from './api.ts'
import type { User } from './types.ts'

2. In-Source Testing

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

// Tests live in the same file!
if (import.meta.vitest) {
  const { it, expect } = import.meta.vitest
  it('adds', () => expect(add(1, 2)).toBe(3))
}

Tests next to the code. Removed in production builds.

3. Built-in Coverage

vitest --coverage

No jest --coverage + istanbul + babel-plugin-istanbul. Just works.

4. UI Mode

vitest --ui

Opens a browser-based test dashboard. See test results, filter, re-run — visually.

Vitest vs Jest in 2026

Feature	Vitest	Jest
ESM support	Native	Experimental
TypeScript	Native	Transform needed
Speed	8-10x faster	Baseline
Config	Reuses vite.config	jest.config
Watch mode	Instant	Slow
UI dashboard	Built-in	Third-party
Coverage	Built-in	Plugin
Mocking	vi.fn()	jest.fn()

When to Stay on Jest

• Large existing test suite (migration cost)
• React Native (Jest has better support)
• No Vite in your build pipeline (Vitest benefits most with Vite)

Get Started

npm install -D vitest
# Add to package.json scripts: "test": "vitest"
npm test

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