FormTestDescriptionForm.php

<?php

namespace Drupal\form_test\Form;

use Drupal\Core\Form\FormBase;
use Drupal\Core\Form\FormStateInterface;

/**
 * Defines a form for testing form element description display options.
 *
 * @internal
 *
 * @see \Drupal\system\Tests\Form\ElementsLabelsTest::testFormDescriptions()
 */
class FormTestDescriptionForm extends FormBase {
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'form_test_description_display';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $form['form_textfield_test_description_before'] = [
            '#type' => 'textfield',
            '#title' => 'Textfield test for description before element',
            '#description' => 'Textfield test for description before element',
            '#description_display' => 'before',
        ];
        $form['form_textfield_test_description_after'] = [
            '#type' => 'textfield',
            '#title' => 'Textfield test for description after element',
            '#description' => 'Textfield test for description after element',
            '#description_display' => 'after',
        ];
        $form['form_textfield_test_description_invisible'] = [
            '#type' => 'textfield',
            '#title' => 'Textfield test for visually-hidden description',
            '#description' => 'Textfield test for visually-hidden description',
            '#description_display' => 'invisible',
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        // The test that uses this form does not submit the form so this is empty.
    }

}