To learn more see {@link http://symfony.com/doc/current/cookbook/bundles/extension.html}
Inheritance: extends Symfony\Component\HttpKernel\DependencyInjection\Extension
 public function testLoadExtension()
 {
     $container = new ContainerBuilder();
     $extension = new AppExtension();
     $extension->load([], $container);
     $resources = $container->getResources();
     $this->assertCount(9, $resources);
     $names = array_map(function (FileResource $resource) {
         $split = explode('/', $resource->getResource());
         return end($split);
     }, $resources);
     $this->assertCount(0, array_diff(['listeners.yml', 'commands.yml', 'redis.yml', 'repositories.yml', 'services.yml', 'validators.yml', 'suggestors.yml'], $names));
 }