VocabularySerializationTestController.php

<?php

declare (strict_types=1);
namespace Drupal\vocabulary_serialization_test;

use Drupal\taxonomy\VocabularyInterface;

/**
 * Controller for testing vocabulary serialization.
 */
class VocabularySerializationTestController {
  public function vocabularyResponse(VocabularyInterface $taxonomy_vocabulary) {
    $response = new VocabularyResponse('this is the output');
    $response->setVocabulary($taxonomy_vocabulary);
    return $response;
  }

}