code: protected function initStorage()
      {
          /** @var DeliveryServerService $deliveryServerService */
          $deliveryServerService = $this->getServiceManager()->get(DeliveryServerService::SERVICE_ID);
          $resultStore = $deliveryServerService->getResultStoreWrapper($this->getTestExecutionUri());
          $testResource = new \core_kernel_classes_Resource($this->getTestDefinitionUri());
          $sessionManager = new \taoQtiTest_helpers_SessionManager($resultStore, $testResource);
  
          $seeker = new BinaryAssessmentTestSeeker($this->getTestDefinition());
          $userUri = $this->getUserUri();
  
          $config = \common_ext_ExtensionsManager::singleton()->getExtensionById('taoQtiTest')->getConfig('testRunner');
          $storageClassName = $config['test-session-storage'];
          $this->storage = new $storageClassName($sessionManager, $seeker, $userUri);
          $this->sessionManager = $sessionManager;
      }
docs: Loads the storage
  @throws \common_exception_Error
  @throws \common_ext_ExtensionException