Issue #3208849 by yogeshmpawar, cilefen, phenaproxima, mohit_aghera, larowlan,...

    $source = $items->getEntity()->getSource();

    $message = $this->t('You can link to media from the following services: @providers', ['@providers' => implode(', ', $source->getProviders())]);

    if (!empty($element['#value']['#description'])) {

    if (!empty($element['value']['#description'])) {

      $element['value']['#description'] = [

        '#theme' => 'item_list',

        '#items' => [$element['value']['#description'], $message],

<?php

namespace Drupal\Tests\media\Functional\FieldWidget;

use Drupal\field\Entity\FieldConfig;

use Drupal\Tests\media\Functional\MediaFunctionalTestBase;

/**

 * @covers \Drupal\media\Plugin\Field\FieldWidget\OEmbedWidget

 *

 * @group media

 */

class OEmbedFieldWidgetTest extends MediaFunctionalTestBase {

  /**

   * {@inheritdoc}

   */

  protected $defaultTheme = 'stark';

  /**

   * Tests that the oEmbed field widget shows the configured help text.

   */

  public function testFieldWidgetHelpText() {

    $account = $this->drupalCreateUser(['create media']);

    $this->drupalLogin($account);

    $media_type = $this->createMediaType('oembed:video');

    $source_field = $media_type->getSource()

      ->getSourceFieldDefinition($media_type)

      ->getName();

    /** @var \Drupal\field\Entity\FieldConfig $field */

    $field = FieldConfig::loadByName('media', $media_type->id(), $source_field);

    $field->setDescription('This is help text for oEmbed field.')

      ->save();

    $this->drupalGet('media/add/' . $media_type->id());

    $assert_session = $this->assertSession();

    $assert_session->pageTextContains('This is help text for oEmbed field.');

    $assert_session->pageTextContains('You can link to media from the following services: YouTube, Vimeo');

  }

}