diff --git a/core/modules/image/src/Tests/Update/ImageUpdateTextFormatsTest.php b/core/modules/image/src/Tests/Update/ImageUpdateTextFormatsTest.php
new file mode 100644
index 0000000000..719e182d45
--- /dev/null
+++ b/core/modules/image/src/Tests/Update/ImageUpdateTextFormatsTest.php
@@ -0,0 +1,47 @@
+<?php
+
+namespace Drupal\image\Tests\Update;
+
+use Drupal\FunctionalTests\Update\UpdatePathTestBase;
+
+/**
+ * Tests Image update path.
+ *
+ * @group image
+ */
+class ImageUpdateTextFormatsTest extends UpdatePathTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setDatabaseDumpFiles() {
+    $this->databaseDumpFiles = [
+      __DIR__ . '/../../../../system/tests/fixtures/update/drupal-8.bare.standard.php.gz',
+    ];
+  }
+
+  /**
+   * Tests image_post_update_enable_filter_image_style().
+   *
+   * @see image_post_update_enable_filter_image_style()
+   */
+  public function testPostUpdateFilterImageStyle() {
+    // Check that the 'basic_html' and 'full_html' formats do not have the image
+    // style filter before starting the update.
+    $config_factory = \Drupal::configFactory();
+    $basic_html_data = $config_factory->get('filter.format.basic_html')->get();
+    $this->assertFalse(isset($basic_html_data['filters']['filter_image_style']), 'Prior to running the update the "filter_image_style" filter is not applied to the basic_html format.');
+    $full_html_data = $config_factory->get('filter.format.full_html')->get();
+    $this->assertFalse(isset($full_html_data['filters']['filter_image_style']), 'Prior to running the update the "filter_image_style" filter is not applied to the full_html format.');
+
+    // Run updates.
+    $this->runUpdates();
+
+    // Check that the filter_format entities have been updated.
+    $basic_html_data = $config_factory->get('filter.format.basic_html')->get();
+    $this->assertTrue(isset($basic_html_data['filters']['filter_image_style']), 'After running the update the "filter_image_style" filter has been applied to the basic_html format.');
+    $full_html_data = $config_factory->get('filter.format.full_html')->get();
+    $this->assertTrue(isset($full_html_data['filters']['filter_image_style']), 'After running the update the "filter_image_style" filter has been applied to the full_html format.');
+  }
+
+}
diff --git a/core/modules/image/tests/src/Functional/FilterImageStyleTest.php b/core/modules/image/tests/src/Functional/FilterImageStyleTest.php
new file mode 100644
index 0000000000..8f7e478767
--- /dev/null
+++ b/core/modules/image/tests/src/Functional/FilterImageStyleTest.php
@@ -0,0 +1,120 @@
+<?php
+
+namespace Drupal\Tests\image\Functional;
+
+use Drupal\Core\Url;
+use Drupal\Tests\BrowserTestBase;
+use Drupal\file\Entity\File;
+use Drupal\filter\Entity\FilterFormat;
+
+/**
+ * Tests FilterImageStyle conversion of inline images to utilize image styles.
+ *
+ * @coversDefaultClass \Drupal\image\Plugin\Filter\FilterImageStyle
+ * @group image
+ */
+class FilterImageStyleTest extends BrowserTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  public static $modules = ['filter', 'file', 'editor', 'node', 'image'];
+
+  /**
+   * A text format allowing images and with FilterImageStyle applied.
+   *
+   * @var \Drupal\Filter\FilterFormatInterface
+   */
+  protected $format;
+
+  /**
+   * Tasks common to all tests.
+   */
+  protected function setUp() {
+    parent::setUp();
+
+    $this->format = FilterFormat::create([
+      'format' => $this->randomMachineName(),
+      'name' => $this->randomString(),
+      'filters' => [
+        'filter_html' => [
+          'status' => TRUE,
+          'settings' => [
+            'allowed_html' => '<img src alt data-entity-type data-entity-uuid data-align data-caption data-image-style width height>',
+          ],
+        ],
+        'filter_image_style' => ['status' => TRUE],
+        'editor_file_reference' => ['status' => TRUE],
+      ],
+    ]);
+    $this->format->save();
+
+    $user = $this->drupalCreateUser(['access content', 'administer nodes']);
+    $this->drupalLogin($user);
+
+    $this->drupalCreateContentType(['type' => 'page', 'name' => 'Basic page']);
+  }
+
+  /**
+   * Helper function to create a test node with configurable image html.
+   */
+  protected function nodeHelper($image_html) {
+    $node = $this->drupalCreateNode([
+      'type' => 'page',
+      'title' => $this->randomString(),
+      'body' => [
+        [
+          'format' => $this->format->id(),
+          'value' => $image_html,
+        ],
+      ],
+    ]);
+    $node->save();
+
+    $this->drupalGet($node->toUrl());
+    $this->assertSession()->statusCodeEquals(200);
+  }
+
+  /**
+   * Tests that images not uploaded through media module are unmolested.
+   */
+  public function testImageNoStyle() {
+    $file_url = Url::fromUri('base:core/themes/bartik/screenshot.png')->toString();
+
+    $image_html = '<img src="' . $file_url . '" width="220">';
+    $this->nodeHelper($image_html);
+
+    /** @var \Behat\Mink\Element\NodeElement $img_element */
+    $image_element = $this->getSession()->getPage()->find('css', "img");
+    $this->assertFalse(empty($image_element));
+
+    $this->assertFalse($image_element->hasAttribute('class'));
+    $this->assertEquals($file_url, $image_element->getAttribute('src'));
+    $this->assertEquals('220', $image_element->getAttribute('width'));
+    $this->assertFalse($image_element->hasAttribute('height'));
+  }
+
+  /**
+   * Tests image style modification of images.
+   */
+  public function testImageStyle() {
+    $this->assertTrue(array_key_exists('medium', $this->container->get('entity_type.manager')->getStorage('image_style')->loadMultiple()));
+
+    $file = File::create(['uri' => 'core/themes/bartik/screenshot.png']);
+    $file->save();
+
+    $image_html = '<img src="' . file_url_transform_relative($file->url()) . '" data-entity-type="file" data-entity-uuid="' . $file->uuid() . '" data-image-style="medium" width="220">';
+    $this->nodeHelper($image_html);
+
+    /** @var \Behat\Mink\Element\NodeElement $img_element */
+    $image_element = $this->getSession()->getPage()->find('css', 'img.image-style-medium');
+    $this->assertFalse(empty($image_element));
+
+    $this->assertTrue(strpos($image_element->getAttribute('src'), 'medium'));
+    $this->assertEquals('220', $image_element->getAttribute('width'));
+    $this->assertEquals('164', $image_element->getAttribute('height'));
+  }
+
+}
diff --git a/core/modules/image/tests/src/FunctionalJavascript/AddImageTest.php b/core/modules/image/tests/src/FunctionalJavascript/AddImageTest.php
new file mode 100644
index 0000000000..25a31993b9
--- /dev/null
+++ b/core/modules/image/tests/src/FunctionalJavascript/AddImageTest.php
@@ -0,0 +1,106 @@
+<?php
+
+namespace Drupal\Tests\image\FunctionalJavascript;
+
+use Drupal\Core\Url;
+use Drupal\FunctionalJavascriptTests\JavascriptTestBase;
+use Drupal\Tests\TestFileCreationTrait;
+use Drupal\editor\Entity\Editor;
+use Drupal\filter\Entity\FilterFormat;
+
+/**
+ * Tests the JavaScript functionality of the drupalimagestyle CKEditor plugin.
+ *
+ * @group image
+ */
+class AddImageTest extends JavascriptTestBase {
+
+  use TestFileCreationTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = ['filter', 'file', 'node', 'image', 'ckeditor'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+
+    $format = FilterFormat::create([
+      'format' => 'filtered_html',
+      'name' => $this->randomString(),
+      'filters' => [
+        'filter_image_style' => ['status' => TRUE],
+      ],
+    ]);
+    $format->save();
+
+    $this->drupalCreateContentType(['type' => 'page', 'name' => 'Basic page']);
+
+    Editor::create([
+      'format' => 'filtered_html',
+      'editor' => 'ckeditor',
+    ])->save();
+
+    $user = $this->drupalCreateUser([
+      'access content',
+      'administer nodes',
+      'create page content',
+      'use text format filtered_html',
+    ]);
+    $this->drupalLogin($user);
+  }
+
+  /**
+   * Tests if an image can be placed inline with the data-image-style attribute.
+   */
+  public function testDataImageStyleElement() {
+    $image_url = Url::fromUri('base:core/themes/bartik/screenshot.png')->toString();
+
+    $this->drupalGet('node/add/page');
+    $this->assertSession()->statusCodeEquals(200);
+
+    $page = $this->getSession()->getPage();
+    // Wait for the ckeditor toolbar elements to appear (loading is done).
+    $image_button_selector = 'a.cke_button__drupalimage';
+    $this->assertJsCondition("jQuery('$image_button_selector').length > 0", 20000);
+    $this->assertSession()->assertWaitOnAjaxRequest();
+
+    $image_button = $page->find('css', $image_button_selector);
+    $this->assertNotEmpty($image_button);
+    $image_button->click();
+    // Wait for the modal form elements to appear (loading is done).
+    $this->assertJsCondition("jQuery('input[data-drupal-selector=\"edit-attributes-alt\"]').length > 0", 20000);
+
+    $url_input = $page->findField('attributes[src]');
+    $this->assertNotEmpty($url_input);
+    $url_input->setValue($image_url);
+
+    $alt_input = $page->findField('attributes[alt]');
+    $this->assertNotEmpty($alt_input);
+    $alt_input->setValue('asd');
+
+    $image_style_input_name = 'attributes[data-image-style]';
+    $this->assertNotEmpty($page->findField($image_style_input_name));
+    $page->selectFieldOption($image_style_input_name, 'thumbnail');
+
+    // To prevent 403s on save, we re-set our request (cookie) state.
+    $this->prepareRequest();
+
+    // Using NodeElement::click() on the button or NodeElement::submit() on the
+    // form generated phantomjs-internal exceptions. This was the only recourse.
+    $script = "jQuery('input[id^=\"edit-actions-save-modal\"]').click()";
+    $this->getSession()->executeScript($script);
+    $this->assertSession()->assertWaitOnAjaxRequest();
+
+    $source_button = $page->find('css', 'a.cke_button__source');
+    $this->assertNotEmpty($source_button);
+    $source_button->click();
+    $this->assertSession()->assertWaitOnAjaxRequest();
+
+    $this->assertContains('data-image-style="thumbnail"', $page->find('css', 'textarea.cke_source')->getValue());
+  }
+
+}
diff --git a/core/modules/image/tests/src/Kernel/EditorImageStyleDialogTest.php b/core/modules/image/tests/src/Kernel/EditorImageStyleDialogTest.php
new file mode 100644
index 0000000000..ab9b71e7ad
--- /dev/null
+++ b/core/modules/image/tests/src/Kernel/EditorImageStyleDialogTest.php
@@ -0,0 +1,169 @@
+<?php
+
+namespace Drupal\Tests\image\Kernel;
+
+use Drupal\Core\Form\FormState;
+use Drupal\Core\Render\RenderContext;
+use Drupal\editor\Entity\Editor;
+use Drupal\editor\Form\EditorImageDialog;
+use Drupal\filter\Entity\FilterFormat;
+use Drupal\KernelTests\Core\Entity\EntityKernelTestBase;
+use Drupal\node\Entity\NodeType;
+
+/**
+ * Tests EditorImageDialog alteration to add image style selection.
+ *
+ * @see image_form_editor_image_dialog_alter()
+ *
+ * @group image
+ */
+class EditorImageStyleDialogTest extends EntityKernelTestBase {
+
+  /**
+   * Editor for testing.
+   *
+   * @var \Drupal\editor\EditorInterface
+   */
+  protected $editor;
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = [
+    'ckeditor',
+    'editor',
+    'editor_test',
+    'file',
+    'image',
+    'node',
+    'system',
+    'user',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+
+    $this->installEntitySchema('file');
+    $this->installSchema('system', ['key_value_expire']);
+    $this->installSchema('node', ['node_access']);
+    $this->installSchema('file', ['file_usage']);
+    $this->installConfig(['node']);
+
+    // Install the image module config so we have the medium image style.
+    $this->installConfig('image');
+
+    // Create a node type for testing.
+    $type = NodeType::create(['type' => 'page', 'name' => 'page']);
+    $type->save();
+    node_add_body_field($type);
+    $this->installEntitySchema('user');
+    $this->container->get('router.builder')->rebuild();
+  }
+
+  /**
+   * Fixture to consolidate tasks while making filter status configurable.
+   *
+   * @param bool $enable_image_filter
+   *   Whether to activate filter_image_style in the text format.
+   *
+   * @return array|\Symfony\Component\HttpFoundation\Response
+   *   The submitted form.
+   */
+  protected function setUpForm($enable_image_filter) {
+    $format = FilterFormat::create([
+      'format' => $this->randomMachineName(),
+      'name' => $this->randomString(),
+      'weight' => 0,
+      'filters' => [
+        'filter_image_style' => ['status' => $enable_image_filter],
+      ],
+    ]);
+    $format->save();
+
+    // Set up text editor.
+    /** @var \Drupal\editor\EditorInterface $editor */
+    $editor = Editor::create([
+      'format' => $format->id(),
+      'editor' => 'ckeditor',
+      'image_upload' => [
+        'max_size' => 100,
+        'scheme' => 'public',
+        'directory' => '',
+        'status' => TRUE,
+      ],
+    ]);
+    $editor->save();
+
+    /** @var \Drupal\file\FileInterface $file */
+    $file = file_save_data(file_get_contents($this->root . '/core/modules/image/sample.png'), 'public://');
+
+    $input = [
+      'editor_object' => [
+        'src' => file_url_transform_relative($file->getFileUri()),
+        'alt' => 'Balloons floating above a field.',
+        'data-entity-type' => 'file',
+        'data-entity-uuid' => $file->uuid(),
+      ],
+      'dialogOptions' => [
+        'title' => 'Edit Image',
+        'dialogClass' => 'editor-image-dialog',
+        'autoResize' => 'true',
+      ],
+      '_drupal_ajax' => '1',
+      'ajax_page_state' => [
+        'theme' => 'bartik',
+        'theme_token' => 'some-token',
+        'libraries' => '',
+      ],
+    ];
+    if ($enable_image_filter) {
+      $input['editor_object']['data-image-style'] = 'medium';
+    }
+
+    $form_state = (new FormState())
+      ->setRequestMethod('POST')
+      ->setUserInput($input)
+      ->addBuildInfo('args', [$editor]);
+
+    /** @var \Drupal\Core\Form\FormBuilderInterface $form_builder */
+    $form_builder = $this->container->get('form_builder');
+    $form_object = new EditorImageDialog(\Drupal::entityTypeManager()->getStorage('file'));
+    $form_id = $form_builder->getFormId($form_object, $form_state);
+    $form = [];
+
+    /** @var \Drupal\Core\Render\RendererInterface $renderer */
+    $renderer = \Drupal::service('renderer');
+    $renderer->executeInRenderContext(new RenderContext(), function () use (&$form, $form_builder, $form_id, $form_state) {
+      $form = $form_builder->retrieveForm($form_id, $form_state);
+      $form_builder->prepareForm($form_id, $form, $form_state);
+      $form_builder->processForm($form_id, $form, $form_state);
+    });
+
+    return $form;
+  }
+
+  /**
+   * Tests that style selection is hidden when filter_image_style is disabled.
+   */
+  public function testDialogNoStyles() {
+    $form = $this->setUpForm(FALSE);
+
+    $this->assertFalse(array_key_exists('image_style', $form));
+  }
+
+  /**
+   * Tests EditorImageDialog when filter_image_style is enabled.
+   */
+  public function testDialogStyles() {
+    $form = $this->setUpForm(TRUE);
+
+    $this->assertEquals(['large', 'medium', 'thumbnail'], array_keys($form['image_style']['selection']['#options']));
+
+    $this->assertEquals('medium', $form['image_style']['selection']['#default_value']);
+    $this->assertEquals(TRUE, $form['image_style']['selection']['#required']);
+  }
+
+}
diff --git a/core/modules/system/tests/src/Functional/Update/FilterHtmlUpdateTest.php b/core/modules/system/tests/src/Functional/Update/FilterHtmlUpdateTest.php
index 09e40aa983..00b72dbca5 100644
--- a/core/modules/system/tests/src/Functional/Update/FilterHtmlUpdateTest.php
+++ b/core/modules/system/tests/src/Functional/Update/FilterHtmlUpdateTest.php
@@ -39,7 +39,7 @@ public function testAllowedHtmlUpdate() {
 
     // Make sure we have the expected values after the update.
     $filters_after = [
-      'basic_html' => '<a href hreflang> <em> <strong> <cite> <blockquote cite> <code> <ul type> <ol start type> <li> <dl> <dt> <dd> <h4 id> <h5 id> <h6 id> <p> <br> <span> <img src alt height width data-align data-caption>',
+      'basic_html' => '<a href hreflang> <em> <strong> <cite> <blockquote cite> <code> <ul type> <ol start type> <li> <dl> <dt> <dd> <h4 id> <h5 id> <h6 id> <p> <br> <span> <img src alt height width data-align data-caption data-image-style>',
       'restricted_html' => '<a href hreflang> <em> <strong> <cite> <blockquote cite> <code> <ul type> <ol start type> <li> <dl> <dt> <dd> <h4 id> <h5 id> <h6 id>',
     ];
     foreach ($filters_after as $name => $after) {