AssetManager\Service\ConcatResolverServiceFactory::createService PHP Method

    public function createService(ServiceLocatorInterface $serviceLocator)
    {
        return $this($serviceLocator, ConcatResolver::class);
    }

 /**
  * Mainly to avoid regressions
  */
 public function testCreateServiceWithNoConfig()
 {
     $serviceManager = new ServiceManager();
     $serviceManager->setService('config', array());
     $factory = new ConcatResolverServiceFactory();
     /* @var ConcatResolver */
     $concatResolver = $factory->createService($serviceManager);
     $this->assertEmpty($concatResolver->getConcats());
 }