Vitest
Next-generation blazing-fast unit testing framework powered by Vite. Compatible with Jest API, supports ESM natively, and runs tests in parallel with HMR. The modern choice for Vite projects.
Why Vitest?
Your project uses Vite (Nuxt, SvelteKit, vanilla Vite)
You want Jest-compatible API with 10x faster cold starts
Modern ESM-first TypeScript project
Signal Breakdown
What drives the Trust Score
Download Trend
Last 12 months
Tradeoffs & Caveats
Know before you commitYou're on Next.js with webpack — Jest has better ecosystem support
You need browser snapshot testing (Playwright is better)
Legacy CJS-heavy codebase — Vitest ESM-first can cause friction
Pricing
Free tier & paid plans
Open source, free forever
N/A
MIT license
Alternative Tools
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Often Used Together
Complementary tools that pair well with Vitest
Learning Resources
Docs, videos, tutorials, and courses
Get Started
Repository and installation options
View on GitHub
github.com/vitest-dev/vitest
npm install --save-dev vitestQuick Start
Copy and adapt to get going fast
// service.test.ts
import { describe, it, expect, vi, beforeEach } from 'vitest';
import { fetchPosts } from './service';
vi.mock('./api', () => ({
apiClient: { get: vi.fn() },
}));
beforeEach(() => vi.clearAllMocks());
describe('fetchPosts', () => {
it('returns posts array', async () => {
const posts = await fetchPosts();
expect(Array.isArray(posts)).toBe(true);
});
});Code Examples
Common usage patterns
Test with vi.mock
Mock a module dependency in Vitest
// notifier.test.ts
import { describe, it, expect, vi } from 'vitest';
import { sendWelcomeEmail } from './notifier';
vi.mock('./mailer', () => ({
sendMail: vi.fn().mockResolvedValue({ messageId: 'abc' }),
}));
it('sends a welcome email on signup', async () => {
await sendWelcomeEmail('alice@example.com');
const { sendMail } = await import('./mailer');
expect(sendMail).toHaveBeenCalledWith(expect.objectContaining({ to: 'alice@example.com' }));
});Benchmark test
Measure performance with Vitest bench
// perf.bench.ts
import { bench, describe } from 'vitest';
import { sortAscending, sortDescending } from './sort';
const arr = Array.from({ length: 1000 }, (_, i) => Math.random());
describe('sorting algorithms', () => {
bench('ascending', () => sortAscending([...arr]));
bench('descending', () => sortDescending([...arr]));
});Community Notes
Real experiences from developers who've used this tool