Vitest Has a Free Test Runner That Replaces Jest — 10x Faster, Native TypeScript, Vite-Powered

The Testing Problem

Jest: slow startup, needs babel transform for TypeScript, fights with ESM. Mocha: no assertions built in. Testing Library: great but needs Jest underneath.

Vitest uses Vite's transform pipeline. Native TypeScript and ESM. 10x faster than Jest. Same API.

What Vitest Gives You

Jest-Compatible API

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

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

  it('handles arrays', () => {
    expect([1, 2, 3]).toContain(2);
    expect([1, 2, 3]).toHaveLength(3);
  });
});

Migrating from Jest? Most tests work without changes.

Native TypeScript

interface User {
  name: string;
  email: string;
}

it('creates a user', () => {
  const user: User = createUser('John', '[e-mail]');
  expect(user.name).toBe('John');
});

No ts-jest. No @babel/preset-typescript. Just write TypeScript.

Watch Mode (Instant)

vitest  # Watch mode by default

Vitest re-runs only affected tests when you save a file. Sub-second feedback.

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 next to the code. Tree-shaken out of production builds.

UI Dashboard

vitest --ui

Visual test dashboard in your browser. See results, filter, re-run.

Coverage

vitest run --coverage

Built-in coverage via v8 or istanbul. No extra config.

Benchmarking

import { bench, describe } from 'vitest';

describe('sort', () => {
  bench('Array.sort', () => {
    [3, 1, 2].sort();
  });

  bench('custom sort', () => {
    customSort([3, 1, 2]);
  });
});

Performance

	Jest	Vitest
Cold start	5-10s	0.3s
100 tests	15s	1.5s
Watch re-run	3-5s	0.1s

Quick Start

npm install -D vitest
npx vitest

Why This Matters

Slow tests mean developers skip tests. Vitest makes testing so fast that there's no excuse not to run them on every save.

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