# src/Service/Test.php
<?php

namespace App\Service;


class Test
{
    public function hello()
    {
        return 'Hello';
    }

}

# config/services.yaml
# Put parameters here that don't need to change on each machine where the app is deployed
# https://symfony.com/doc/current/best_practices/configuration.html#application-related-configuration
parameters:

services:
    # default configuration for services in *this* file
    _defaults:
        # automatically injects dependencies in your services
        autowire: true
        # automatically registers your services as commands, event subscribers, etc.
        autoconfigure: true
        # this means you cannot fetch services directly from the container via $container->get()
        # if you need to do this, you can override this setting on individual services
        public: false

    # makes classes in src/ available to be used as services
    # this creates a service per class whose id is the fully-qualified class name
    App\:
        resource: '../src/*'
        # you can exclude directories or files
        # but if a service is unused, it's removed anyway
        exclude: '../src/{DataFixtures,Entity,Migrations,Tests}'

    # controllers are imported separately to make sure they
    # have the tag that allows actions to type-hint services
    App\Controller\:
        resource: '../src/Controller'
        tags: ['controller.service_arguments']

    App\Services\Test:
        class: 'App\Service\Test'
        public: true

# src/Controller/DefaultController.php
<?php

namespace App\Controller;


use App\Service\Test;
use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\Routing\Annotation\Route;

class DefaultController extends AbstractController
{
    /**
     * @Route("/", name="default")
     */
    public function index()
    {
        $this->get(Test::class);
        return new Response('Hello');
    }
}