Issues/3396669: has-error class not applied to media fields

Closes #3396669

core/modules/media_library/tests/src/FunctionalJavascript/EntityReferenceWidgetTest.php

@@ -490,6 +490,10 @@ public function testRequiredMediaField(): void {
     $assert_session->pageTextNotContains('This value should not be null.');
     $assert_session->pageTextContains(sprintf('%s field is required.', $field_config->label()));
 
+    // Check if 'error' class has been added to media field.
+    $media_field = $assert_session->elementExists('css', '#field_unlimited_media-media-library-wrapper');
+    $this->assertTrue($media_field->hasClass('error'));
+
     // Open the media library, select an item and save the node.
     $this->openMediaLibraryForField('field_unlimited_media');
     $this->selectMediaItem(0);