config_pages-8.x-2.8/tests/modules/config_pages_test/config_pages_test.module

<?php

/**
 * @file
 * Test module for Config Pages access control.
 */

use Drupal\Core\Access\AccessResult;
use Drupal\Core\Entity\EntityInterface;
use Drupal\Core\Session\AccountInterface;

/**
 * Implements hook_ENTITY_TYPE_access().
 */
function config_pages_test_config_pages_access(EntityInterface $entity, $operation, AccountInterface $account) {
  // Deny all access for testing purposes.
  if ($operation === 'update' && $entity->bundle() === 'test_access_type') {
    return AccessResult::forbidden('Access denied by test module for security testing.');
  }
  return AccessResult::neutral();
}