Issue #3078030 by danflanagan8, mottihoresh, Abhijith S, smustgrave, andypost,...

  public function settingsSummary() {

    $summary = parent::settingsSummary();

    $link_types = [

      'content' => $this->t('Linked to content'),

      'media' => $this->t('Linked to media item'),

    ];

    // Display this setting only if image is linked.

    $image_link_setting = $this->getSetting('image_link');

    if (isset($link_types[$image_link_setting])) {

      $summary[] = $link_types[$image_link_setting];

    // The parent class adds summary text if the image_link setting is

    // 'content'. Here we only have to add summary text if the setting

    // is 'media'.

    if ($this->getSetting('image_link') === 'media') {

      $summary[] = $this->t('Linked to media item');

    }

    return $summary;

<?php

namespace Drupal\Tests\media\Kernel;

use Drupal\entity_test\Entity\EntityTestBundle;

use Drupal\Tests\field\Traits\EntityReferenceTestTrait;

/**

 * @coversDefaultClass \Drupal\media\Plugin\Field\FieldFormatter\MediaThumbnailFormatter

 * @group media

 */

class MediaThumbnailFormatterTest extends MediaKernelTestBase {

  use EntityReferenceTestTrait;

  /**

   * Modules to install.

   *

   * @var array

   */

  protected static $modules = [

    'entity_test',

  ];

  /**

   * Test media reference field name.

   *

   * @var string

   */

  protected $mediaFieldName = 'field_media';

  /**

   * Test entity type id.

   *

   * @var string

   */

  protected $testEntityTypeId = 'entity_test_with_bundle';

  /**

   * Test entity bundle id.

   *

   * @var string

   */

  protected $testEntityBundleId = 'entity_test_bundle';

  /**

   * {@inheritdoc}

   */

  protected function setUp(): void {

    parent::setUp();

    // Create an entity bundle that has a media reference field.

    $entity_test_bundle = EntityTestBundle::create([

      'id' => $this->testEntityBundleId,

    ]);

    $entity_test_bundle->save();

    $this->createEntityReferenceField(

      $this->testEntityTypeId,

      $this->testEntityBundleId,

      $this->mediaFieldName,

      $this->mediaFieldName,

      'media'

    );

  }

  /**

   * Tests the settings summary.

   *

   * @param array $settings

   *   The settings to use for the formatter.

   * @param array $expected_summary

   *   The expected settings summary.

   *

   * @covers ::settingsSummary

   *

   * @dataProvider providerTestSettingsSummary

   */

  public function testSettingsSummary(array $settings, array $expected_summary): void {

    /** @var \Drupal\Core\Entity\Display\EntityViewDisplayInterface $display  */

    $display = \Drupal::service('entity_display.repository')->getViewDisplay($this->testEntityTypeId, $this->testEntityBundleId);

    $display->setComponent($this->mediaFieldName, [

      'type' => 'media_thumbnail',

      'settings' => $settings,

    ]);

    $formatter = $display->getRenderer($this->mediaFieldName);

    $actual_summary = array_map('strval', $formatter->settingsSummary());

    $this->assertSame($expected_summary, $actual_summary);

  }

  /**

   * Data provider for testSettingsSummary().

   *

   * @return array[]

   */

  public function providerTestSettingsSummary(): array {

    return [

      'link to content' => [

        [

          'image_link' => 'content',

        ],

        [

          'Original image',

          'Linked to content',

          'Image loading: lazy',

        ],

      ],

      'link to media' => [

        [

          'image_link' => 'media',

        ],

        [

          'Original image',

          'Image loading: lazy',

          'Linked to media item',

        ],

      ],

      'link to nothing' => [

        [

          'image_link' => '',

        ],

        [

          'Original image',

          'Image loading: lazy',

        ],

      ],

    ];

  }

}