Project Structure with autoload

Folders as plugins

Put shared plugins in plugins/ and route modules in routes/, then let autoload register them.

// src/app.js
import AutoLoad from '@fastify/autoload';
import { join } from 'node:path';

export default async function app(fastify, opts) {
  fastify.register(AutoLoad, { dir: join(import.meta.dirname, 'plugins') });
  fastify.register(AutoLoad, { dir: join(import.meta.dirname, 'routes'), options: { prefix: '/api' } });
}

Export build() from app.js and call listen only in server.js. Tests can then import the app and use inject without opening a port.