diff --git a/core/modules/media/src/Annotation/MediaSource.php b/core/modules/media/src/Annotation/MediaSource.php
index 59f9e29ba0..2440ebec53 100644
--- a/core/modules/media/src/Annotation/MediaSource.php
+++ b/core/modules/media/src/Annotation/MediaSource.php
@@ -80,6 +80,20 @@ class MediaSource extends Plugin {
   public $thumbnail_uri_metadata_attribute = 'thumbnail_uri';
 
   /**
+   * The metadata attribute name to provide the thumbnail alt.
+   *
+   * @var string|null
+   */
+  public $thumbnail_alt_metadata_attribute;
+
+  /**
+   * The metadata attribute name to provide the thumbnail title.
+   *
+   * @var string|null
+   */
+  public $thumbnail_title_metadata_attribute;
+
+  /**
    * The metadata attribute name to provide the default name.
    *
    * @var string
diff --git a/core/modules/media/src/Entity/Media.php b/core/modules/media/src/Entity/Media.php
index f05c1c937e..9c389235ab 100644
--- a/core/modules/media/src/Entity/Media.php
+++ b/core/modules/media/src/Entity/Media.php
@@ -163,8 +163,22 @@ protected function updateThumbnail($from_queue = FALSE) {
       $this->thumbnail->target_id = $file->id();
     }
 
-    $this->thumbnail->alt = $this->t('Thumbnail');
-    $this->thumbnail->title = $this->label();
+    // Set the image alt.
+    $plugin_definition = $this->getSource()->getPluginDefinition();
+    if (!empty($plugin_definition['thumbnail_alt_metadata_attribute'])) {
+      $this->thumbnail->alt = $this->getSource()->getMetadata($this, $plugin_definition['thumbnail_alt_metadata_attribute']);
+    }
+    else {
+      $this->thumbnail->alt = $this->t('Thumbnail');
+    }
+
+    // Set the image title.
+    if (!empty($plugin_definition['thumbnail_title_metadata_attribute'])) {
+      $this->thumbnail->title = $this->getSource()->getMetadata($this, $plugin_definition['thumbnail_title_metadata_attribute']);
+    }
+    else {
+      $this->thumbnail->title = $this->label();
+    }
 
     return $this;
   }
@@ -234,11 +248,7 @@ protected function sourceFieldChanged() {
   protected function shouldUpdateThumbnail($is_new = FALSE) {
     // Update thumbnail if we don't have a thumbnail yet or when the source
     // field value changes.
-    if (!$this->get('thumbnail')->entity || $is_new || $this->sourceFieldChanged()) {
-      return TRUE;
-    }
-
-    return FALSE;
+    return !$this->get('thumbnail')->entity || $is_new || $this->sourceFieldChanged();
   }
 
   /**
diff --git a/core/modules/media/src/Entity/MediaType.php b/core/modules/media/src/Entity/MediaType.php
index 796e892b53..5000f24114 100644
--- a/core/modules/media/src/Entity/MediaType.php
+++ b/core/modules/media/src/Entity/MediaType.php
@@ -218,4 +218,12 @@ public function getFieldMap() {
     return $this->field_map;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function setFieldMap($map) {
+    $this->field_map = $map;
+    return $this;
+  }
+
 }
diff --git a/core/modules/media/src/MediaSourceBase.php b/core/modules/media/src/MediaSourceBase.php
index 2fe0880af3..2f117b066a 100644
--- a/core/modules/media/src/MediaSourceBase.php
+++ b/core/modules/media/src/MediaSourceBase.php
@@ -132,7 +132,6 @@ public function getMetadata(MediaInterface $media, $attribute_name) {
       case 'thumbnail_uri':
         $default_thumbnail_filename = $this->pluginDefinition['default_thumbnail_filename'];
         return $this->configFactory->get('media.settings')->get('icon_base_uri') . '/' . $default_thumbnail_filename;
-
     }
   }
 
diff --git a/core/modules/media/src/MediaTypeInterface.php b/core/modules/media/src/MediaTypeInterface.php
index af775c9b8b..7d1bf291f3 100644
--- a/core/modules/media/src/MediaTypeInterface.php
+++ b/core/modules/media/src/MediaTypeInterface.php
@@ -83,4 +83,15 @@ public function setNewRevision($new_revision);
    */
   public function getFieldMap();
 
+  /**
+   * Sets the metadata field map.
+   *
+   * @param array $map
+   *   Field mapping with metadata attribute names as keys and entity field
+   *   names as values.
+   *
+   * @return $this
+   */
+  public function setFieldMap($map);
+
 }
diff --git a/core/modules/media/tests/modules/media_test_source/src/Plugin/media/Source/Test.php b/core/modules/media/tests/modules/media_test_source/src/Plugin/media/Source/Test.php
index 3b6085776a..2e6653559d 100644
--- a/core/modules/media/tests/modules/media_test_source/src/Plugin/media/Source/Test.php
+++ b/core/modules/media/tests/modules/media_test_source/src/Plugin/media/Source/Test.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\media_test_source\Plugin\media\Source;
 
+use Drupal\Component\Utility\NestedArray;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\media\MediaInterface;
 use Drupal\media\MediaSourceBase;
@@ -22,25 +23,37 @@ class Test extends MediaSourceBase {
    * {@inheritdoc}
    */
   public function getMetadataAttributes() {
-    return [
-      'attribute_1' => $this->t('Attribute 1'),
-      'attribute_2' => $this->t('Attribute 2'),
-    ];
+    $attributes = \Drupal::state()->get('media_source_test_attributes', [
+      'attribute_1' => ['label' => $this->t('Attribute 1'), 'value' => 'Value 1'],
+      'attribute_2' => ['label' => $this->t('Attribute 2'), 'value' => 'Value 1'],
+    ]);
+    return array_map(function ($item) {return $item['label'];}, $attributes);
   }
 
   /**
    * {@inheritdoc}
    */
   public function getMetadata(MediaInterface $media, $attribute_name) {
-    switch ($attribute_name) {
+    $attributes = \Drupal::state()->get('media_source_test_attributes', [
+      'attribute_1' => ['label' => $this->t('Attribute 1'), 'value' => 'Value 1'],
+      'attribute_2' => ['label' => $this->t('Attribute 2'), 'value' => 'Value 1'],
+    ]);
 
-      case 'thumbnail_uri':
-        return DRUPAL_ROOT . '/core/misc/druplicon.png';
+    if (in_array($attribute_name, array_keys($attributes))) {
+      return $attributes[$attribute_name]['value'];
+    }
 
-      default:
-        return parent::getMetadata($media, $attribute_name);
+    return parent::getMetadata($media, $attribute_name);
+  }
 
-    }
+  /**
+   * {@inheritdoc}
+   */
+  public function getPluginDefinition() {
+    return NestedArray::mergeDeep(
+      parent::getPluginDefinition(),
+      \Drupal::state()->get('media_source_test_definition', [])
+    );
   }
 
   /**
diff --git a/core/modules/media/tests/src/Functional/MediaUiFunctionalTest.php b/core/modules/media/tests/src/Functional/MediaUiFunctionalTest.php
index b868cab39e..21fe5e486c 100644
--- a/core/modules/media/tests/src/Functional/MediaUiFunctionalTest.php
+++ b/core/modules/media/tests/src/Functional/MediaUiFunctionalTest.php
@@ -164,38 +164,4 @@ public function testMediaWithMultipleMediaTypes() {
     $assert_session->pageTextContains($second_media_item->label());
   }
 
-  /**
-   * Tests the queue worker for media item thumbnails.
-   */
-  public function testMediaThumbnailQueueWorker() {
-    // Tests and creates the media type with queued thumbnails.
-    $media_type = $this->createMediaType(['queue_thumbnail_downloads' => TRUE]);
-
-    // Create a media item.
-    $media_item = Media::create(['bundle' => $media_type->id()]);
-    $media_item->save();
-
-    $filename = $media_item->getSource()->getPluginDefinition()['default_thumbnail_filename'];
-    $default_thumb_uri = \Drupal::service('config.factory')->get('media.settings')->get('icon_base_uri') . '/' . $filename;
-    $source_thumb_uri = $media_item->getSource()->getMetadata($media_item, $media_item->getSource()->getPluginDefinition()['thumbnail_uri_metadata_attribute']);
-
-    // Media thumbnail should be the default image.
-    $this->assertEquals($default_thumb_uri, $media_item->get('thumbnail')->entity->getFileUri());
-
-    // Check if queue item was created.
-    $queue_name = 'media_entity_thumbnail';
-    $queue_worker = \Drupal::service('plugin.manager.queue_worker')->createInstance($queue_name);
-    $queue = \Drupal::queue($queue_name);
-    $item = $queue->claimItem();
-    $this->assertEquals($media_item->id(), $item->data['id']);
-
-    // Process queue worker.
-    $queue_worker->processItem($item->data);
-    $queue->deleteItem($item);
-
-    // Load updated media item to check changed thumbnail.
-    $updated_media_item = Media::load($media_item->id());
-    $this->assertEquals($source_thumb_uri, $updated_media_item->get('thumbnail')->entity->getFileUri());
-  }
-
 }
diff --git a/core/modules/media/tests/src/Kernel/BasicCreationTest.php b/core/modules/media/tests/src/Kernel/BasicCreationTest.php
index b0cd2f59f8..5e0ab64481 100644
--- a/core/modules/media/tests/src/Kernel/BasicCreationTest.php
+++ b/core/modules/media/tests/src/Kernel/BasicCreationTest.php
@@ -2,7 +2,6 @@
 
 namespace Drupal\Tests\media\Kernel;
 
-use Drupal\KernelTests\KernelTestBase;
 use Drupal\media\Entity\Media;
 use Drupal\media\Entity\MediaType;
 use Drupal\media\MediaInterface;
@@ -13,60 +12,7 @@
  *
  * @group media
  */
-class BasicCreationTest extends KernelTestBase {
-
-  /**
-   * Modules to install.
-   *
-   * @var array
-   */
-  public static $modules = [
-    'media',
-    'media_test_source',
-    'image',
-    'user',
-    'field',
-    'system',
-    'file',
-  ];
-
-  /**
-   * The test media type.
-   *
-   * @var \Drupal\media\MediaTypeInterface
-   */
-  protected $testMediaType;
-
-  /**
-   * {@inheritdoc}
-   */
-  protected function setUp() {
-    parent::setUp();
-
-    $this->installEntitySchema('user');
-    $this->installEntitySchema('file');
-    $this->installSchema('file', 'file_usage');
-    $this->installEntitySchema('media');
-    $this->installConfig(['field', 'system', 'image', 'file']);
-
-    // Create a test media type.
-    $id = strtolower($this->randomMachineName());
-    $this->testMediaType = MediaType::create([
-      'id' => $id,
-      'label' => $id,
-      'source' => 'test',
-      'new_revision' => FALSE,
-    ]);
-    $this->testMediaType->save();
-
-    $source_field = $this->testMediaType->getSource()->createSourceField($this->testMediaType);
-    $source_field->getFieldStorageDefinition()->save();
-    $source_field->save();
-
-    $this->testMediaType->set('source_configuration', [
-      'source_field' => $source_field->getName(),
-    ])->save();
-  }
+class BasicCreationTest extends MediaKernelTestBase {
 
   /**
    * Tests creating a media type programmatically.
@@ -107,16 +53,6 @@ public function testMediaEntityCreation() {
     $this->assertEquals('Unnamed', $media->label(), 'The media item was not created with the correct name.');
     $source_field_name = $media->bundle->entity->getSource()->getSourceFieldDefinition($media->bundle->entity)->getName();
     $this->assertEquals('Nation of sheep, ruled by wolves, owned by pigs.', $media->get($source_field_name)->value, 'Source returns correct source field.');
-
-    // Test the creation of a media item without user-defined label and
-    // check if a default name is provided.
-    $media = Media::create([
-      'bundle' => $this->testMediaType->id(),
-    ]);
-    $media->save();
-    $expected_name = 'media' . ':' . $this->testMediaType->id() . ':' . $media->uuid();
-    $this->assertEquals($this->testMediaType->id(), $media->bundle(), 'The media item was not created with correct type.');
-    $this->assertEquals($expected_name, $media->label(), 'The media item was not created with a default name.');
   }
 
 }
diff --git a/core/modules/media/tests/src/Kernel/MediaKernelTestBase.php b/core/modules/media/tests/src/Kernel/MediaKernelTestBase.php
new file mode 100644
index 0000000000..e13150e0ff
--- /dev/null
+++ b/core/modules/media/tests/src/Kernel/MediaKernelTestBase.php
@@ -0,0 +1,66 @@
+<?php
+
+namespace Drupal\Tests\media\Kernel;
+
+use Drupal\KernelTests\KernelTestBase;
+use Drupal\media\Entity\MediaType;
+
+/**
+ * Base class for Media kernel tests.
+ */
+abstract class MediaKernelTestBase extends KernelTestBase {
+
+  /**
+   * Modules to install.
+   *
+   * @var array
+   */
+  public static $modules = [
+    'media',
+    'media_test_source',
+    'image',
+    'user',
+    'field',
+    'system',
+    'file',
+  ];
+
+  /**
+   * The test media type.
+   *
+   * @var \Drupal\media\MediaTypeInterface
+   */
+  protected $testMediaType;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+
+    $this->installEntitySchema('user');
+    $this->installEntitySchema('file');
+    $this->installSchema('file', 'file_usage');
+    $this->installEntitySchema('media');
+    $this->installConfig(['field', 'system', 'image', 'file', 'media']);
+
+    // Create a test media type.
+    $id = strtolower($this->randomMachineName());
+    $this->testMediaType = MediaType::create([
+      'id' => $id,
+      'label' => $id,
+      'source' => 'test',
+      'new_revision' => FALSE,
+    ]);
+    $this->testMediaType->save();
+
+    $source_field = $this->testMediaType->getSource()->createSourceField($this->testMediaType);
+    $source_field->getFieldStorageDefinition()->save();
+    $source_field->save();
+
+    $this->testMediaType->set('source_configuration', [
+      'source_field' => $source_field->getName(),
+    ])->save();
+  }
+
+}
diff --git a/core/modules/media/tests/src/Kernel/MediaSourceTest.php b/core/modules/media/tests/src/Kernel/MediaSourceTest.php
new file mode 100644
index 0000000000..14349c69aa
--- /dev/null
+++ b/core/modules/media/tests/src/Kernel/MediaSourceTest.php
@@ -0,0 +1,231 @@
+<?php
+
+namespace Drupal\Tests\media\Kernel;
+
+use Drupal\media\Entity\Media;
+
+/**
+ * Tests media source plugins related logic.
+ *
+ * @group media
+ */
+class MediaSourceTest extends MediaKernelTestBase {
+
+  /**
+   * Tests default media name functionality.
+   */
+  public function testDefaultName() {
+    // Make sure that the default name is set if not provided by the user.
+    /** @var \Drupal\media\MediaInterface $media */
+    $media = Media::create(['bundle' => $this->testMediaType->id()]);
+    $this->assertEquals('default_name', $media->getSource()->getPluginDefinition()['default_name_metadata_attribute'], 'Default metadata attribute is used for the default name.');
+    $this->assertEquals('media:' . $media->bundle() . ':' . $media->uuid(), $media->getSource()->getMetadata($media, 'default_name'), 'Value of the default name metadata attribute looks correct.');
+    $media->save();
+    $this->assertEquals('media:' . $media->bundle() . ':' . $media->uuid(), $media->label(), 'Default name was set correctly.');
+
+    // Make sure that the user-supplied name is used.
+    /** @var \Drupal\media\MediaInterface $media */
+    $name = 'User-supplied name';
+    $media = Media::create([
+      'bundle' => $this->testMediaType->id(),
+      'name' => $name,
+    ]);
+    $this->assertEquals('default_name', $media->getSource()->getPluginDefinition()['default_name_metadata_attribute'], 'Default metadata attribute is used for the default name.');
+    $this->assertEquals('media:' . $media->bundle() . ':' . $media->uuid(), $media->getSource()->getMetadata($media, 'default_name'), 'Value of the default name metadata attribute looks correct.');
+    $media->save();
+    $this->assertEquals($name, $media->label(), 'User-supplied name was set correctly.');
+
+    // Change the default name attribute and see if it is used to set the name.
+    $name = 'Old Major';
+    \Drupal::state()->set('media_source_test_attributes', ['alternative_name' => ['title' => 'Alternative name', 'value' => $name]]);
+    \Drupal::state()->set('media_source_test_definition', ['default_name_metadata_attribute' => 'alternative_name']);
+    /** @var \Drupal\media\MediaInterface $media */
+    $media = Media::create(['bundle' => $this->testMediaType->id()]);
+    $this->assertEquals('alternative_name', $media->getSource()->getPluginDefinition()['default_name_metadata_attribute'], 'Correct metadata attribute is used for the default name.');
+    $this->assertEquals($name, $media->getSource()->getMetadata($media, 'alternative_name'), 'Value of the default name metadata attribute looks correct.');
+    $media->save();
+    $this->assertEquals($name, $media->label(), 'Default name was set correctly.');
+  }
+
+  /**
+   * Tests metadata mapping functionality.
+   */
+  public function testMetadataMapping() {
+    $field_name = 'field_to_map_to';
+    $attribute_name = 'attribute_to_map';
+    $storage = $this->container->get('entity_type.manager')
+      ->getStorage('field_storage_config')
+      ->create([
+        'entity_type' => 'media',
+        'field_name' => $field_name,
+        'type' => 'string',
+      ]);
+    $storage->save();
+
+    $this->container->get('entity_type.manager')
+      ->getStorage('field_config')
+      ->create([
+        'field_storage' => $storage,
+        'bundle' => $this->testMediaType->id(),
+        'label' => 'Field to map to',
+      ])->save();
+
+    // Save the entity without defining the metadata mapping and check that the
+    // field stays empty.
+    /** @var \Drupal\media\MediaInterface $media */
+    $media = Media::create([
+      'bundle' => $this->testMediaType->id(),
+      'field_media_test' => 'some_value',
+    ]);
+    $media->save();
+    $this->assertEmpty($media->get($field_name)->value, 'Field stayed empty.');
+
+    // Define mapping and make sure that the value was stored in the field.
+    \Drupal::state()->set('media_source_test_attributes', [
+      $attribute_name => ['title' => 'Attribute to map', 'value' => 'Snowball']
+    ]);
+    $this->testMediaType->setFieldMap([$attribute_name => $field_name])->save();
+    $media = Media::create([
+      'bundle' => $this->testMediaType->id(),
+      'field_media_test' => 'some_value',
+    ]);
+    $this->assertEquals('Snowball', $media->getSource()->getMetadata($media, $attribute_name), 'Value of the metadata attribute is correct.');
+    $media->save();
+    $this->assertEquals('Snowball', $media->get($field_name)->value, 'Metadata attribute was correctly mapped to the field.');
+
+    // Change the metadata attribute value and re-save the entity. Field value
+    // should stay the same.
+    \Drupal::state()->set('media_source_test_attributes', [
+      $attribute_name => ['title' => 'Attribute to map', 'value' => 'Pinkeye']
+    ]);
+    $this->assertEquals('Pinkeye', $media->getSource()->getMetadata($media, $attribute_name), 'Value of the metadata attribute is correct.');
+    $media->save();
+    $this->assertEquals('Snowball', $media->get($field_name)->value, 'Metadata attribute was correctly mapped to the field.');
+
+    // Now change the value of the source field and make sure that the mapped
+    // values update too.
+    $this->assertEquals('Pinkeye', $media->getSource()->getMetadata($media, $attribute_name), 'Value of the metadata attribute is correct.');
+    $media->set('field_media_test', 'some_new_value');
+    $media->save();
+    $this->assertEquals('Pinkeye', $media->get($field_name)->value, 'Metadata attribute was correctly mapped to the field.');
+  }
+
+  /**
+   * Tests the default thumbnail functionality.
+   */
+  public function testThumbnail() {
+    file_put_contents('public://thumbnail1.jpg', '');
+    file_put_contents('public://thumbnail2.jpg', '');
+
+    // Save a media entity and make sure thumbnail was added.
+    \Drupal::state()->set('media_source_test_attributes', [
+      'thumbnail_uri' => ['title' => 'Thumbnail', 'value' => 'public://thumbnail1.jpg'],
+    ]);
+    /** @var \Drupal\media\MediaInterface $media */
+    $media = Media::create([
+      'bundle' => $this->testMediaType->id(),
+      'name' => 'Mr. Jones',
+      'field_media_test' => 'some_value',
+    ]);
+    $this->assertEquals('public://thumbnail1.jpg', $media->getSource()->getMetadata($media, 'thumbnail_uri'), 'Value of the thumbnail metadata attribute is correct.');
+    $media->save();
+    $this->assertEquals('public://thumbnail1.jpg', $media->thumbnail->entity->getFileUri(), 'Thumbnail was added to the media entity.');
+    $this->assertEquals('Mr. Jones', $media->thumbnail->title, 'Title text was set on the thumbnail.');
+    $this->assertEquals('Thumbnail', $media->thumbnail->alt, 'Alt text was set on the thumbnail.');
+
+    // Now change the metadata attribute and make sure that the thumbnail stays
+    // the same.
+    \Drupal::state()->set('media_source_test_attributes', [
+      'thumbnail_uri' => ['title' => 'Thumbnail', 'value' => 'public://thumbnail2.jpg'],
+    ]);
+    $this->assertEquals('public://thumbnail2.jpg', $media->getSource()->getMetadata($media, 'thumbnail_uri'), 'Value of the thumbnail metadata attribute is correct.');
+    $media->save();
+    $this->assertEquals('public://thumbnail1.jpg', $media->thumbnail->entity->getFileUri(), 'Thumbnail was preserved.');
+
+    // Remove the thumbnail and make sure that it is auto-updated on save.
+    $media->thumbnail->target_id = NULL;
+    $this->assertEquals('public://thumbnail2.jpg', $media->getSource()->getMetadata($media, 'thumbnail_uri'), 'Value of the thumbnail metadata attribute is correct.');
+    $media->save();
+    $this->assertEquals('public://thumbnail2.jpg', $media->thumbnail->entity->getFileUri(), 'New thumbnail was added to the media entity.');
+
+    // Change the metadata attribute again, change the source field value and
+    // make sure that the thumbnail updates too.
+    \Drupal::state()->set('media_source_test_attributes', [
+      'thumbnail_uri' => ['title' => 'Thumbnail', 'value' => 'public://thumbnail1.jpg'],
+    ]);
+    $media->field_media_test->value = 'some_new_value';
+    $this->assertEquals('public://thumbnail1.jpg', $media->getSource()->getMetadata($media, 'thumbnail_uri'), 'Value of the thumbnail metadata attribute is correct.');
+    $media->save();
+    $this->assertEquals('public://thumbnail1.jpg', $media->thumbnail->entity->getFileUri(), 'New thumbnail was added to the media entity.');
+
+    // Change the thumbnail metadata attribute and make sure that the thumbnail
+    // is set correctly.
+    \Drupal::state()->set('media_source_test_attributes', [
+      'thumbnail_uri' => ['title' => 'Should not be used', 'value' => 'public://thumbnail1.jpg'],
+      'alternative_thumbnail_uri' => ['title' => 'Should be used', 'value' => 'public://thumbnail2.jpg'],
+    ]);
+    \Drupal::state()->set('media_source_test_definition', ['thumbnail_uri_metadata_attribute' => 'alternative_thumbnail_uri']);
+    $media = Media::create([
+      'bundle' => $this->testMediaType->id(),
+      'name' => 'Mr. Jones',
+      'field_media_test' => 'some_value',
+    ]);
+    $this->assertEquals('public://thumbnail1.jpg', $media->getSource()->getMetadata($media, 'thumbnail_uri'), 'Value of the metadata attribute is correct.');
+    $this->assertEquals('public://thumbnail2.jpg', $media->getSource()->getMetadata($media, 'alternative_thumbnail_uri'), 'Value of the thumbnail metadata attribute is correct.');
+    $media->save();
+    $this->assertEquals('public://thumbnail2.jpg', $media->thumbnail->entity->getFileUri(), 'Correct metadata attribute was used for the thumbnail.');
+
+    // Enable queued thumbnails and make sure that the entity gets the default
+    // thumbnail initially.
+    \Drupal::state()->set('media_source_test_definition', []);
+    \Drupal::state()->set('media_source_test_attributes', [
+      'thumbnail_uri' => ['title' => 'Should not be used', 'value' => 'public://thumbnail1.jpg'],
+    ]);
+    $this->testMediaType->setQueueThumbnailDownloadsStatus(TRUE)->save();
+    $media = Media::create([
+      'bundle' => $this->testMediaType->id(),
+      'name' => 'Mr. Jones',
+      'field_media_test' => 'some_value',
+    ]);
+    $this->assertEquals('public://thumbnail1.jpg', $media->getSource()->getMetadata($media, 'thumbnail_uri'), 'Value of the metadata attribute is correct.');
+    $media->save();
+    $this->assertEquals('public://media-icons/generic/generic.png', $media->thumbnail->entity->getFileUri(), 'Default thumbnail was set initially.');
+
+    // Process the queue item and make sure that the thumbnail was updated too.
+    $queue_name = 'media_entity_thumbnail';
+    /** @var \Drupal\Core\Queue\QueueWorkerInterface $queue_worker */
+    $queue_worker = \Drupal::service('plugin.manager.queue_worker')->createInstance($queue_name);
+    $queue = \Drupal::queue($queue_name);
+    $this->assertEquals(1, $queue->numberOfItems(), 'Item was added to the queue.');
+
+    $item = $queue->claimItem();
+    $this->assertEquals($media->id(), $item->data['id'], 'Queue item that was created belongs to the correct entity.');
+
+    $queue_worker->processItem($item->data);
+    $queue->deleteItem($item);
+    $this->assertEquals(0, $queue->numberOfItems(), 'Item was removed from the queue.');
+
+    $media = Media::load($media->id());
+    $this->assertEquals('public://thumbnail1.jpg', $media->thumbnail->entity->getFileUri(), 'Thumbnail was updated by the queue.');
+
+    // Set alt and title metadata attributes and make sure they are used for the
+    // thumbnail.
+    \Drupal::state()->set('media_source_test_definition', [
+      'thumbnail_alt_metadata_attribute' => 'alt',
+      'thumbnail_title_metadata_attribute' => 'title',
+    ]);
+    \Drupal::state()->set('media_source_test_attributes', [
+      'alt' => ['title' => 'Alt text', 'value' => 'This will be alt.'],
+      'title' => ['title' => 'Title text', 'value' => 'This will be title.'],
+    ]);
+    $media = Media::create([
+      'bundle' => $this->testMediaType->id(),
+      'name' => 'Boxer',
+      'field_media_test' => 'some_value',
+    ]);
+    $media->save();
+    $this->assertEquals('Boxer', $media->label(), 'Correct name was set on the media entity.');
+    $this->assertEquals('This will be title.', $media->thumbnail->title, 'Title text was set on the thumbnail.');
+    $this->assertEquals('This will be alt.', $media->thumbnail->alt, 'Alt text was set on the thumbnail.');
+  }
+}