update

web/core/modules/image/image.module

@@ -248,6 +248,7 @@ function image_path_flush($path) {
  *
  * @param $include_empty
  *   If TRUE a '- None -' option will be inserted in the options array.
+ *
  * @return
  *   Array of image styles both key and value are set to style name.
  */

web/core/modules/image/tests/modules/image_module_test/src/Plugin/Field/FieldFormatter/DummyImageFormatter.php

@@ -0,0 +1,33 @@
+<?php
+
+namespace Drupal\image_module_test\Plugin\Field\FieldFormatter;
+
+use Drupal\Core\Field\FieldItemListInterface;
+use Drupal\Core\Field\FormatterBase;
+
+/**
+ * Plugin implementation of the Dummy image formatter.
+ *
+ * @FieldFormatter(
+ *   id = "dummy_image_formatter",
+ *   label = @Translation("Dummy image"),
+ *   field_types = {
+ *     "image"
+ *   },
+ *   quickedit = {
+ *     "editor" = "image"
+ *   }
+ * )
+ */
+class DummyImageFormatter extends FormatterBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function viewElements(FieldItemListInterface $items, $langcode) {
+    return [
+      ['#markup' => 'Dummy'],
+    ];
+  }
+
+}

web/core/modules/image/tests/src/Functional/ImageFieldTestBase.php

@@ -49,7 +49,19 @@ abstract class ImageFieldTestBase extends BrowserTestBase {
       $this->drupalCreateContentType(['type' => 'article', 'name' => 'Article']);
     }
 
-    $this->adminUser = $this->drupalCreateUser(['access content', 'access administration pages', 'administer site configuration', 'administer content types', 'administer node fields', 'administer nodes', 'create article content', 'edit any article content', 'delete any article content', 'administer image styles', 'administer node display']);
+    $this->adminUser = $this->drupalCreateUser([
+      'access content',
+      'access administration pages',
+      'administer site configuration',
+      'administer content types',
+      'administer node fields',
+      'administer nodes',
+      'create article content',
+      'edit any article content',
+      'delete any article content',
+      'administer image styles',
+      'administer node display',
+    ]);
     $this->drupalLogin($this->adminUser);
   }