/**
  * @return \OpenClassrooms\ServiceProxy\ServiceProxyBuilderInterface
  */
 protected function getServiceProxyBuilder($cacheDir = null)
 {
     $serviceProxyBuilder = new ServiceProxyBuilder();
     $configuration = new Configuration();
     $configuration->setProxiesTargetDir($cacheDir);
     $serviceProxyBuilder->setProxyFactory($this->buildProxyFactory($configuration));
     return $serviceProxyBuilder;
 }