Callbacks.php

<?php

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

use Drupal\Core\Form\FormStateInterface;

/**
 * Simple object with callbacks.
 */
class Callbacks {
    
    /**
     * Validation handler for the entity_test entity form.
     */
    public static function entityTestFormValidate(array &$form, FormStateInterface $form_state) : void {
        $form['#entity_test_form_validate'] = TRUE;
    }
    
    /**
     * Validation handler for the entity_test entity form.
     */
    public static function entityTestFormValidateCheck(array &$form, FormStateInterface $form_state) : void {
        if (!empty($form['#entity_test_form_validate'])) {
            \Drupal::state()->set('entity_test.form.validate.result', TRUE);
        }
    }

}