FilterTestStatic.php

<?php

declare (strict_types=1);
namespace Drupal\filter_test_plugin\Plugin\Filter;

use Drupal\Core\StringTranslation\TranslatableMarkup;
use Drupal\filter\Attribute\Filter;
use Drupal\filter\FilterProcessResult;
use Drupal\filter\Plugin\FilterBase;
use Drupal\filter\Plugin\FilterInterface;

/**
 * Provides a filter that returns the same static text.
 */
class FilterTestStatic extends FilterBase {
  
  /**
   * {@inheritdoc}
   */
  public function process($text, $langcode) {
    return new FilterProcessResult('filtered text');
  }

}