npm install --save-dev wrangler miniflare @cloudflare/vitest-pool-workers vitest

wrangler dev --local        # workerd locally; no remote calls
wrangler dev                # default = local-mode in Wrangler 3+

import { Miniflare } from 'miniflare';

const mf = new Miniflare({
  scriptPath: './src/worker.js',
  modules: true,
  kvNamespaces: ['MY_KV'],
  d1Databases: ['DB'],
  r2Buckets: ['MY_BUCKET'],
  durableObjects: {
    COUNTER: 'Counter',
  },
});

const res = await mf.dispatchFetch('https://example.com/');
expect(res.status).toBe(200);
expect(await res.text()).toBe('Hello');

await mf.dispose();

// vitest.config.ts
import { defineWorkersConfig } from '@cloudflare/vitest-pool-workers/config';

export default defineWorkersConfig({
  test: {
    poolOptions: {
      workers: {
        wrangler: { configPath: './wrangler.toml' },
      },
    },
  },
});

// src/worker.test.ts
import { env, SELF } from 'cloudflare:test';
import { expect, test } from 'vitest';

test('responds with hello', async () => {
  const response = await SELF.fetch('https://example.com/');
  expect(await response.text()).toBe('Hello');
});

test('writes to KV', async () => {
  await env.MY_KV.put('key', 'value');
  expect(await env.MY_KV.get('key')).toBe('value');
});

import { env } from 'cloudflare:test';

test('counter increments', async () => {
  const id = env.COUNTER.idFromName('test');
  const stub = env.COUNTER.get(id);
  const r1 = await stub.fetch('https://example.com/increment');
  expect(await r1.text()).toBe('1');
  const r2 = await stub.fetch('https://example.com/increment');
  expect(await r2.text()).toBe('2');
});

import { env } from 'cloudflare:test';

test('d1 query', async () => {
  await env.DB.exec('CREATE TABLE IF NOT EXISTS users (id INT, name TEXT)');
  await env.DB.prepare('INSERT INTO users VALUES (?, ?)').bind(1, 'alice').run();
  const { results } = await env.DB.prepare('SELECT * FROM users').all();
  expect(results).toEqual([{ id: 1, name: 'alice' }]);
});

npx vitest run                # @cloudflare/vitest-pool-workers
wrangler dev                  # CLI dev

jobs:
  workers-tests:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v5
      - uses: actions/setup-node@v4
        with: { node-version: '20' }
      - run: npm ci
      - run: npx vitest run