Behat\Testwork\ServiceContainer\ExtensionManager::activateExtension PHP Method

    public function activateExtension($locator)
    {
        $extension = $this->initialize($locator);
        $this->debugInformation['extensions_list'][] = $extension->getConfigKey();
        return $this->extensions[$extension->getConfigKey()] = $extension;
    }

 /**
  * Initializes extensions using provided config.
  *
  * @param ContainerBuilder $container
  * @param array            $configs
  *
  * @return array
  */
 private function initializeExtensions(ContainerBuilder $container, array $configs)
 {
     foreach ($configs as $i => $config) {
         if (isset($config['extensions'])) {
             foreach ($config['extensions'] as $extensionLocator => $extensionConfig) {
                 $extension = $this->extensionManager->activateExtension($extensionLocator);
                 $configs[$i][$extension->getConfigKey()] = $extensionConfig;
             }
             unset($configs[$i]['extensions']);
         }
     }
     $this->extensionManager->initializeExtensions();
     $container->setParameter('extensions', $this->extensionManager->getExtensionClasses());
     return $configs;
 }