Symfony DiC: register new Definition

gistfile1.php

<?php

use Symfony\Component\DependencyInjection\DefinitionDecorator;
use Symfony\Component\HttpKernel\DependencyInjection\Extension;
use Symfony\Component\DependencyInjection\Loader\XmlFileLoader;
use Symfony\Component\DependencyInjection\Reference;
use Symfony\Component\DependencyInjection\ContainerInterface;
use Symfony\Component\DependencyInjection\ContainerBuilder;

// ...

        $exampleDef = new DefinitionDecorator('coo_example.service_name');

        $exampleDef
            ->addArgument(new Reference('doctrine', ContainerInterface::NULL_ON_INVALID_REFERENCE))
            ->addTag('doctrine.event_subscriber')
        ;

        $container->setDefinition('coo_example.service_name.test', $exampleDef);

// ...