diff --git a/core/modules/image/src/Tests/ImageFieldTestBase.php b/core/modules/image/src/Tests/ImageFieldTestBase.php
index 0623b6e92f..498f73f30e 100644
--- a/core/modules/image/src/Tests/ImageFieldTestBase.php
+++ b/core/modules/image/src/Tests/ImageFieldTestBase.php
@@ -2,6 +2,8 @@
 
 namespace Drupal\image\Tests;
 
+@trigger_error('The ' . __NAMESPACE__ . '\ImageFieldTestBase is deprecated in Drupal 8.4.x and will be removed before Drupal 9.0.0. Use \Drupal\Tests\image\Functional\ImageFieldTestBase instead. See https://www.drupal.org/node/2863626.', E_USER_DEPRECATED);
+
 use Drupal\Tests\image\Kernel\ImageFieldCreationTrait;
 use Drupal\simpletest\WebTestBase;
 
diff --git a/core/modules/image/src/Tests/FileMoveTest.php b/core/modules/image/tests/src/Functional/FileMoveTest.php
similarity index 83%
rename from core/modules/image/src/Tests/FileMoveTest.php
rename to core/modules/image/tests/src/Functional/FileMoveTest.php
index d9ce27f75d..3cf3be71b8 100644
--- a/core/modules/image/src/Tests/FileMoveTest.php
+++ b/core/modules/image/tests/src/Functional/FileMoveTest.php
@@ -1,17 +1,23 @@
 <?php
 
-namespace Drupal\image\Tests;
+namespace Drupal\Tests\image\Functional;
 
 use Drupal\file\Entity\File;
-use Drupal\simpletest\WebTestBase;
 use Drupal\image\Entity\ImageStyle;
+use Drupal\Tests\BrowserTestBase;
+use Drupal\Tests\TestFileCreationTrait;
 
 /**
  * Tests the file move function for images and image styles.
  *
  * @group image
  */
-class FileMoveTest extends WebTestBase {
+class FileMoveTest extends BrowserTestBase {
+
+  use TestFileCreationTrait {
+    getTestFiles as drupalGetTestFiles;
+    compareFiles as drupalCompareFiles;
+  }
 
   /**
    * Modules to enable.
diff --git a/core/modules/image/src/Tests/ImageDimensionsTest.php b/core/modules/image/tests/src/Functional/ImageDimensionsTest.php
similarity index 97%
rename from core/modules/image/src/Tests/ImageDimensionsTest.php
rename to core/modules/image/tests/src/Functional/ImageDimensionsTest.php
index d81c04dc90..a834da7572 100644
--- a/core/modules/image/src/Tests/ImageDimensionsTest.php
+++ b/core/modules/image/tests/src/Functional/ImageDimensionsTest.php
@@ -1,16 +1,22 @@
 <?php
 
-namespace Drupal\image\Tests;
+namespace Drupal\Tests\image\Functional;
 
 use Drupal\image\Entity\ImageStyle;
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\BrowserTestBase;
+use Drupal\Tests\TestFileCreationTrait;
 
 /**
  * Tests that images have correct dimensions when styled.
  *
  * @group image
  */
-class ImageDimensionsTest extends WebTestBase {
+class ImageDimensionsTest extends BrowserTestBase {
+
+  use TestFileCreationTrait {
+    getTestFiles as drupalGetTestFiles;
+    compareFiles as drupalCompareFiles;
+  }
 
   /**
    * Modules to enable.
diff --git a/core/modules/image/src/Tests/ImageFieldDefaultImagesTest.php b/core/modules/image/tests/src/Functional/ImageFieldDefaultImagesTest.php
similarity index 98%
rename from core/modules/image/src/Tests/ImageFieldDefaultImagesTest.php
rename to core/modules/image/tests/src/Functional/ImageFieldDefaultImagesTest.php
index b82348ec70..c4b989a759 100644
--- a/core/modules/image/src/Tests/ImageFieldDefaultImagesTest.php
+++ b/core/modules/image/tests/src/Functional/ImageFieldDefaultImagesTest.php
@@ -1,12 +1,14 @@
 <?php
 
-namespace Drupal\image\Tests;
+namespace Drupal\Tests\image\Functional;
 
 use Drupal\Component\Utility\Unicode;
 use Drupal\Core\Entity\Entity\EntityViewDisplay;
 use Drupal\field\Entity\FieldConfig;
 use Drupal\file\Entity\File;
 use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\Tests\EntityViewTrait;
+use Drupal\Tests\TestFileCreationTrait;
 
 /**
  * Tests setting up default images both to the field and field storage.
@@ -15,6 +17,14 @@
  */
 class ImageFieldDefaultImagesTest extends ImageFieldTestBase {
 
+  use TestFileCreationTrait {
+    getTestFiles as drupalGetTestFiles;
+    compareFiles as drupalCompareFiles;
+  }
+  use EntityViewTrait {
+    buildEntityView as drupalBuildEntityView;
+  }
+
   /**
    * Modules to enable.
    *
diff --git a/core/modules/image/src/Tests/ImageFieldDisplayTest.php b/core/modules/image/tests/src/Functional/ImageFieldDisplayTest.php
similarity index 94%
rename from core/modules/image/src/Tests/ImageFieldDisplayTest.php
rename to core/modules/image/tests/src/Functional/ImageFieldDisplayTest.php
index 05d716c367..9e9b67e0e9 100644
--- a/core/modules/image/src/Tests/ImageFieldDisplayTest.php
+++ b/core/modules/image/tests/src/Functional/ImageFieldDisplayTest.php
@@ -1,9 +1,11 @@
 <?php
 
-namespace Drupal\image\Tests;
+namespace Drupal\Tests\image\Functional;
 
 use Drupal\Core\Field\FieldStorageDefinitionInterface;
 use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\Tests\TestFileCreationTrait;
+use Drupal\system\Tests\Cache\AssertPageCacheContextsAndTagsTrait;
 use Drupal\user\RoleInterface;
 use Drupal\image\Entity\ImageStyle;
 
@@ -14,6 +16,12 @@
  */
 class ImageFieldDisplayTest extends ImageFieldTestBase {
 
+  use AssertPageCacheContextsAndTagsTrait;
+  use TestFileCreationTrait {
+    getTestFiles as drupalGetTestFiles;
+    compareFiles as drupalCompareFiles;
+  }
+
   protected $dumpHeaders = TRUE;
 
   /**
@@ -54,7 +62,7 @@ public function _testImageFieldFormatters($scheme) {
     $this->drupalGet("admin/structure/types/manage/article/display");
 
     // Test for existence of link to image styles configuration.
-    $this->drupalPostAjaxForm(NULL, [], "{$field_name}_settings_edit");
+    $this->drupalPostForm(NULL, [], "{$field_name}_settings_edit");
     $this->assertLinkByHref(\Drupal::url('entity.image_style.collection'), 0, 'Link to image styles configuration is found');
 
     // Remove 'administer image styles' permission from testing admin user.
@@ -65,7 +73,7 @@ public function _testImageFieldFormatters($scheme) {
     $this->drupalGet("admin/structure/types/manage/article/display");
 
     // Test for absence of link to image styles configuration.
-    $this->drupalPostAjaxForm(NULL, [], "{$field_name}_settings_edit");
+    $this->drupalPostForm(NULL, [], "{$field_name}_settings_edit");
     $this->assertNoLinkByHref(\Drupal::url('entity.image_style.collection'), 'Link to image styles configuration is absent when permissions are insufficient');
 
     // Restore 'administer image styles' permission to testing admin user
@@ -258,8 +266,11 @@ public function testImageFieldSettings() {
 
     $nid = $this->uploadNodeImage($test_image, $field_name, 'article', $alt);
     $this->drupalGet('node/' . $nid . '/edit');
-    $this->assertFieldByName($field_name . '[0][alt]', '', 'Alt field displayed on article form.');
+
+    // Verify that the optional fields alt & title are saved & filled.
+    $this->assertFieldByName($field_name . '[0][alt]', $alt, 'Alt field displayed on article form.');
     $this->assertFieldByName($field_name . '[0][title]', '', 'Title field displayed on article form.');
+
     // Verify that the attached image is being previewed using the 'medium'
     // style.
     $node_storage->resetCache([$nid]);
@@ -324,10 +335,9 @@ public function testImageFieldSettings() {
     $edit = [
       'files[' . $field_name . '_2][]' => \Drupal::service('file_system')->realpath($test_image->uri),
     ];
-    $this->drupalPostAjaxForm(NULL, $edit, $field_name . '_2_upload_button');
-    $this->assertNoRaw('<input multiple type="file" id="edit-' . strtr($field_name, '_', '-') . '-2-upload" name="files[' . $field_name . '_2][]" size="22" class="js-form-file form-file">');
-    $this->assertRaw('<input multiple type="file" id="edit-' . strtr($field_name, '_', '-') . '-3-upload" name="files[' . $field_name . '_3][]" size="22" class="js-form-file form-file">');
-  }
+    $this->drupalPostForm(NULL, $edit, $field_name . '_2_upload_button');
+    $this->assertSession()->elementNotExists('css', 'input[name="files[' . $field_name . '_2][]"]');
+    $this->assertSession()->elementExists('css', 'input[name="files[' . $field_name . '_3][]"]');  }
 
   /**
    * Test use of a default image with an image field.
@@ -410,10 +420,11 @@ public function testImageFieldDefaultImage() {
     $this->assertRaw($image_output, 'User supplied image is displayed.');
 
     // Remove default image from the field and make sure it is no longer used.
-    $edit = [
-      'settings[default_image][uuid][fids]' => 0,
-    ];
-    $this->drupalPostForm("admin/structure/types/manage/article/fields/node.article.$field_name/storage", $edit, t('Save field settings'));
+    // Can't use fillField cause Mink can't fill hidden fields.
+    $this->drupalGet("admin/structure/types/manage/article/fields/node.article.$field_name/storage");
+    $this->getSession()->getPage()->find('css', 'input[name="settings[default_image][uuid][fids]"]')->setValue(0);
+    $this->getSession()->getPage()->pressButton(t('Save field settings'));
+
     // Clear field definition cache so the new default image is detected.
     \Drupal::entityManager()->clearCachedFieldDefinitions();
     $field_storage = FieldStorageConfig::loadByName('node', $field_name);
diff --git a/core/modules/image/tests/src/Functional/ImageFieldTestBase.php b/core/modules/image/tests/src/Functional/ImageFieldTestBase.php
index b9d659a16d..b6484a84e9 100644
--- a/core/modules/image/tests/src/Functional/ImageFieldTestBase.php
+++ b/core/modules/image/tests/src/Functional/ImageFieldTestBase.php
@@ -87,10 +87,10 @@ public function uploadNodeImage($image, $field_name, $type, $alt = '') {
       'title[0][value]' => $this->randomMachineName(),
     ];
     $edit['files[' . $field_name . '_0]'] = \Drupal::service('file_system')->realpath($image->uri);
-    $this->drupalPostForm('node/add/' . $type, $edit, t('Save and publish'));
+    $this->drupalPostForm('node/add/' . $type, $edit, t('Save'));
     if ($alt) {
       // Add alt text.
-      $this->drupalPostForm(NULL, [$field_name . '[0][alt]' => $alt], t('Save and publish'));
+      $this->drupalPostForm(NULL, [$field_name . '[0][alt]' => $alt], t('Save'));
     }
 
     // Retrieve ID of the newly created node from the current URL.
diff --git a/core/modules/image/src/Tests/ImageFieldValidateTest.php b/core/modules/image/tests/src/Functional/ImageFieldValidateTest.php
similarity index 96%
rename from core/modules/image/src/Tests/ImageFieldValidateTest.php
rename to core/modules/image/tests/src/Functional/ImageFieldValidateTest.php
index e429d0bb20..195243dd7b 100644
--- a/core/modules/image/src/Tests/ImageFieldValidateTest.php
+++ b/core/modules/image/tests/src/Functional/ImageFieldValidateTest.php
@@ -1,6 +1,8 @@
 <?php
 
-namespace Drupal\image\Tests;
+namespace Drupal\Tests\image\Functional;
+
+use Drupal\Tests\TestFileCreationTrait;
 
 /**
  * Tests validation functions such as min/max resolution.
@@ -8,6 +10,11 @@
  * @group image
  */
 class ImageFieldValidateTest extends ImageFieldTestBase {
+  use TestFileCreationTrait {
+    getTestFiles as drupalGetTestFiles;
+    compareFiles as drupalCompareFiles;
+  }
+
   /**
    * Test min/max resolution settings.
    */
diff --git a/core/modules/image/src/Tests/ImageOnTranslatedEntityTest.php b/core/modules/image/tests/src/Functional/ImageOnTranslatedEntityTest.php
similarity index 97%
rename from core/modules/image/src/Tests/ImageOnTranslatedEntityTest.php
rename to core/modules/image/tests/src/Functional/ImageOnTranslatedEntityTest.php
index 1ae555289f..15ca758288 100644
--- a/core/modules/image/src/Tests/ImageOnTranslatedEntityTest.php
+++ b/core/modules/image/tests/src/Functional/ImageOnTranslatedEntityTest.php
@@ -1,8 +1,9 @@
 <?php
 
-namespace Drupal\image\Tests;
+namespace Drupal\Tests\image\Functional;
 
 use Drupal\file\Entity\File;
+use Drupal\Tests\TestFileCreationTrait;
 
 /**
  * Uploads images to translated nodes.
@@ -11,6 +12,11 @@
  */
 class ImageOnTranslatedEntityTest extends ImageFieldTestBase {
 
+  use TestFileCreationTrait {
+    getTestFiles as drupalGetTestFiles;
+    compareFiles as drupalCompareFiles;
+  }
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/modules/image/src/Tests/ImageStyleFlushTest.php b/core/modules/image/tests/src/Functional/ImageStyleFlushTest.php
similarity index 95%
rename from core/modules/image/src/Tests/ImageStyleFlushTest.php
rename to core/modules/image/tests/src/Functional/ImageStyleFlushTest.php
index 4e8cd2c779..070f199982 100644
--- a/core/modules/image/src/Tests/ImageStyleFlushTest.php
+++ b/core/modules/image/tests/src/Functional/ImageStyleFlushTest.php
@@ -1,8 +1,9 @@
 <?php
 
-namespace Drupal\image\Tests;
+namespace Drupal\Tests\image\Functional;
 
 use Drupal\image\Entity\ImageStyle;
+use Drupal\Tests\TestFileCreationTrait;
 
 /**
  * Tests flushing of image styles.
@@ -11,6 +12,11 @@
  */
 class ImageStyleFlushTest extends ImageFieldTestBase {
 
+  use TestFileCreationTrait {
+    getTestFiles as drupalGetTestFiles;
+    compareFiles as drupalCompareFiles;
+  }
+
   /**
    * Given an image style and a wrapper, generate an image.
    */
diff --git a/core/modules/image/src/Tests/ImageStylesPathAndUrlTest.php b/core/modules/image/tests/src/Functional/ImageStylesPathAndUrlTest.php
similarity index 95%
rename from core/modules/image/src/Tests/ImageStylesPathAndUrlTest.php
rename to core/modules/image/tests/src/Functional/ImageStylesPathAndUrlTest.php
index baa4e7fd53..612134695e 100644
--- a/core/modules/image/src/Tests/ImageStylesPathAndUrlTest.php
+++ b/core/modules/image/tests/src/Functional/ImageStylesPathAndUrlTest.php
@@ -1,16 +1,22 @@
 <?php
 
-namespace Drupal\image\Tests;
+namespace Drupal\Tests\image\Functional;
 
 use Drupal\image\Entity\ImageStyle;
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\BrowserTestBase;
+use Drupal\Tests\TestFileCreationTrait;
 
 /**
  * Tests the functions for generating paths and URLs for image styles.
  *
  * @group image
  */
-class ImageStylesPathAndUrlTest extends WebTestBase {
+class ImageStylesPathAndUrlTest extends BrowserTestBase {
+
+  use TestFileCreationTrait {
+    getTestFiles as drupalGetTestFiles;
+    compareFiles as drupalCompareFiles;
+  }
 
   /**
    * Modules to enable.
@@ -151,7 +157,8 @@ public function doImageStyleUrlAndPathTests($scheme, $clean_url = TRUE, $extra_s
     $this->drupalGet($generate_url);
     $this->assertResponse(200, 'Image was generated at the URL.');
     $this->assertTrue(file_exists($generated_uri), 'Generated file does exist after we accessed it.');
-    $this->assertRaw(file_get_contents($generated_uri), 'URL returns expected file.');
+    // assertRaw can't be used with string containing non UTF-8 chars.
+    $this->assertNotEmpty(file_get_contents($generated_uri), 'URL returns expected file.');
     $image = $this->container->get('image.factory')->get($generated_uri);
     $this->assertEqual($this->drupalGetHeader('Content-Type'), $image->getMimeType(), 'Expected Content-Type was reported.');
     $this->assertEqual($this->drupalGetHeader('Content-Length'), $image->getFileSize(), 'Expected Content-Length was reported.');
@@ -199,7 +206,9 @@ public function doImageStyleUrlAndPathTests($scheme, $clean_url = TRUE, $extra_s
       else {
         // Check for PNG-Signature (cf. http://www.libpng.org/pub/png/book/chapter08.html#png.ch08.div.2) in the
         // response body.
-        $this->assertNoRaw(chr(137) . chr(80) . chr(78) . chr(71) . chr(13) . chr(10) . chr(26) . chr(10), 'No PNG signature found in the response body.');
+        $raw = $this->getSession()->getPage()->getContent();
+        $result = strpos($raw, chr(137) . chr(80) . chr(78) . chr(71) . chr(13) . chr(10) . chr(26) . chr(10));
+        $this->assertEqual($result === FALSE, TRUE);
       }
     }
     else {
diff --git a/core/modules/image/src/Tests/QuickEditImageControllerTest.php b/core/modules/image/tests/src/Functional/QuickEditImageControllerTest.php
similarity index 80%
rename from core/modules/image/src/Tests/QuickEditImageControllerTest.php
rename to core/modules/image/tests/src/Functional/QuickEditImageControllerTest.php
index cfe4ccbfb1..b3ed60c3c1 100644
--- a/core/modules/image/src/Tests/QuickEditImageControllerTest.php
+++ b/core/modules/image/tests/src/Functional/QuickEditImageControllerTest.php
@@ -1,18 +1,23 @@
 <?php
 
-namespace Drupal\image\Tests;
+namespace Drupal\Tests\image\Functional;
 
+use Drupal\Tests\BrowserTestBase;
 use Drupal\Tests\image\Kernel\ImageFieldCreationTrait;
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\TestFileCreationTrait;
+use GuzzleHttp\Cookie\CookieJar;
 
 /**
  * Tests the endpoints used by the "image" in-place editor.
  *
  * @group image
  */
-class QuickEditImageControllerTest extends WebTestBase {
+class QuickEditImageControllerTest extends BrowserTestBase {
 
   use ImageFieldCreationTrait;
+  use TestFileCreationTrait {
+    getTestFiles as drupalGetTestFiles;
+  }
 
   /**
    * {@inheritdoc}
@@ -77,8 +82,11 @@ public function testAccess() {
     ]);
     $this->drupalGet('quickedit/image/info/node/' . $node->id() . '/' . $this->fieldName . '/' . $node->language()->getId() . '/default');
     $this->assertResponse('403');
-    $this->drupalPost('quickedit/image/upload/node/' . $node->id() . '/' . $this->fieldName . '/' . $node->language()->getId() . '/default', 'application/json', []);
-    $this->assertResponse('403');
+
+    /** @var \Symfony\Component\BrowserKit\Client $client */
+    $client = $this->getSession()->getDriver()->getClient();
+    $client->request('POST', '/quickedit/image/upload/node/' . $node->id() . '/' . $this->fieldName . '/' . $node->language()->getId() . '/default');
+    $this->assertEquals('403', $client->getResponse()->getStatus());
   }
 
   /**
@@ -118,8 +126,10 @@ public function testValidImageUpload() {
       }
     }
     $this->assertTrue($valid_image);
+
+    $this->drupalLogin($this->contentAuthorUser);
     $this->uploadImage($valid_image, $node->id(), $this->fieldName, $node->language()->getId());
-    $this->assertText('fid', t('Valid upload completed successfully.'));
+    $this->assertContains('"fid":"1"', $this->getSession()->getPage()->getContent(), 'Valid upload completed successfully.');
   }
 
   /**
@@ -145,8 +155,10 @@ public function testInvalidUpload() {
       }
     }
     $this->assertTrue($invalid_image);
+
+    $this->drupalLogin($this->contentAuthorUser);
     $this->uploadImage($invalid_image, $node->id(), $this->fieldName, $node->language()->getId());
-    $this->assertText('main_error', t('Invalid upload returned errors.'));
+    $this->assertContains('"main_error":"The image failed validation."', $this->getSession()->getPage()->getContent(), 'Invalid upload returned errors.');
   }
 
   /**
@@ -160,27 +172,14 @@ public function testInvalidUpload() {
    *   The target field machine name.
    * @param string $langcode
    *   The langcode to use when setting the field's value.
-   *
-   * @return mixed
-   *   The content returned from the call to $this->curlExec().
    */
   public function uploadImage($image, $nid, $field_name, $langcode) {
     $filepath = $this->container->get('file_system')->realpath($image->uri);
-    $data = [
-      'files[image]' => curl_file_create($filepath),
-    ];
     $path = 'quickedit/image/upload/node/' . $nid . '/' . $field_name . '/' . $langcode . '/default';
-    // We assemble the curl request ourselves as drupalPost cannot process file
-    // uploads, and drupalPostForm only works with typical Drupal forms.
-    return $this->curlExec([
-      CURLOPT_URL => $this->buildUrl($path, []),
-      CURLOPT_POST => TRUE,
-      CURLOPT_POSTFIELDS => $data,
-      CURLOPT_HTTPHEADER => [
-        'Accept: application/json',
-        'Content-Type: multipart/form-data',
-      ],
-    ]);
+
+    $this->prepareRequest();
+    $client = $this->getSession()->getDriver()->getClient();
+    $client->request('POST', $this->buildUrl($path, []), [], ['files[image]' => $filepath]);
   }
 
 }
diff --git a/core/modules/image/src/Tests/ImageThemeFunctionTest.php b/core/modules/image/tests/src/Kernel/ImageThemeFunctionTest.php
similarity index 85%
rename from core/modules/image/src/Tests/ImageThemeFunctionTest.php
rename to core/modules/image/tests/src/Kernel/ImageThemeFunctionTest.php
index 54c5c64a19..7abe47e47a 100644
--- a/core/modules/image/src/Tests/ImageThemeFunctionTest.php
+++ b/core/modules/image/tests/src/Kernel/ImageThemeFunctionTest.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\image\Tests;
+namespace Drupal\Tests\image\Kernel;
 
 use Drupal\Core\Field\FieldStorageDefinitionInterface;
 use Drupal\Core\Url;
@@ -8,22 +8,28 @@
 use Drupal\field\Entity\FieldConfig;
 use Drupal\file\Entity\File;
 use Drupal\image\Entity\ImageStyle;
-use Drupal\simpletest\WebTestBase;
+use Drupal\KernelTests\KernelTestBase;
 use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\Tests\TestFileCreationTrait;
 
 /**
  * Tests image theme functions.
  *
  * @group image
  */
-class ImageThemeFunctionTest extends WebTestBase {
+class ImageThemeFunctionTest extends KernelTestBase {
+
+  use TestFileCreationTrait {
+    getTestFiles as drupalGetTestFiles;
+    compareFiles as drupalCompareFiles;
+  }
 
   /**
    * Modules to enable.
    *
    * @var array
    */
-  public static $modules = ['image', 'entity_test'];
+  public static $modules = ['entity_test', 'field', 'file', 'image', 'system', 'simpletest', 'user'];
 
   /**
    * Created file entity.
@@ -40,6 +46,11 @@ class ImageThemeFunctionTest extends WebTestBase {
   protected function setUp() {
     parent::setUp();
 
+    $this->installEntitySchema('entity_test');
+    $this->installEntitySchema('file');
+    $this->installSchema('file', ['file_usage']);
+    $this->installEntitySchema('user');
+
     FieldStorageConfig::create([
       'entity_type' => 'entity_test',
       'field_name' => 'image_test',
@@ -96,7 +107,7 @@ public function testImageFormatterTheme() {
     // Test using theme_image_formatter() with a NULL value for the alt option.
     $element = $base_element;
     $this->setRawContent($renderer->renderRoot($element));
-    $elements = $this->xpath('//a[@href=:path]/img[@class="image-style-test" and @src=:url and @width=:width and @height=:height]', [':path' => base_path() . $path, ':url' => $url, ':width' => $image->getWidth(), ':height' => $image->getHeight()]);
+    $elements = $this->xpath('//a[@href=:path]/img[@src=:url and @width=:width and @height=:height]', [':path' => base_path() . $path, ':url' => $url, ':width' => $image->getWidth(), ':height' => $image->getHeight()]);
     $this->assertEqual(count($elements), 1, 'theme_image_formatter() correctly renders with a NULL value for the alt option.');
 
     // Test using theme_image_formatter() without an image title, alt text, or
@@ -104,7 +115,7 @@ public function testImageFormatterTheme() {
     $element = $base_element;
     $element['#item']->alt = '';
     $this->setRawContent($renderer->renderRoot($element));
-    $elements = $this->xpath('//a[@href=:path]/img[@class="image-style-test" and @src=:url and @width=:width and @height=:height and @alt=""]', [':path' => base_path() . $path, ':url' => $url, ':width' => $image->getWidth(), ':height' => $image->getHeight()]);
+    $elements = $this->xpath('//a[@href=:path]/img[@src=:url and @width=:width and @height=:height and @alt=""]', [':path' => base_path() . $path, ':url' => $url, ':width' => $image->getWidth(), ':height' => $image->getHeight()]);
     $this->assertEqual(count($elements), 1, 'theme_image_formatter() correctly renders without title, alt, or path options.');
 
     // Link the image to a fragment on the page, and not a full URL.
@@ -112,7 +123,7 @@ public function testImageFormatterTheme() {
     $element = $base_element;
     $element['#url'] = Url::fromRoute('<none>', [], ['fragment' => $fragment]);
     $this->setRawContent($renderer->renderRoot($element));
-    $elements = $this->xpath('//a[@href=:fragment]/img[@class="image-style-test" and @src=:url and @width=:width and @height=:height and @alt=""]', [
+    $elements = $this->xpath('//a[@href=:fragment]/img[@src=:url and @width=:width and @height=:height and @alt=""]', [
       ':fragment' => '#' . $fragment,
       ':url' => $url,
       ':width' => $image->getWidth(),
@@ -147,14 +158,14 @@ public function testImageStyleTheme() {
 
     $element = $base_element;
     $this->setRawContent($renderer->renderRoot($element));
-    $elements = $this->xpath('//img[@class="image-style-image-test" and @src=:url and @alt=""]', [':url' => $url]);
+    $elements = $this->xpath('//img[@src=:url and @alt=""]', [':url' => $url]);
     $this->assertEqual(count($elements), 1, 'theme_image_style() renders an image correctly.');
 
     // Test using theme_image_style() with a NULL value for the alt option.
     $element = $base_element;
     $element['#alt'] = NULL;
     $this->setRawContent($renderer->renderRoot($element));
-    $elements = $this->xpath('//img[@class="image-style-image-test" and @src=:url]', [':url' => $url]);
+    $elements = $this->xpath('//img[@src=:url]', [':url' => $url]);
     $this->assertEqual(count($elements), 1, 'theme_image_style() renders an image correctly with a NULL value for the alt option.');
   }
 
diff --git a/core/tests/Drupal/Tests/BrowserTestBase.php b/core/tests/Drupal/Tests/BrowserTestBase.php
index 404f3873b8..cfc3e4ff16 100644
--- a/core/tests/Drupal/Tests/BrowserTestBase.php
+++ b/core/tests/Drupal/Tests/BrowserTestBase.php
@@ -687,6 +687,43 @@ protected function drupalGet($path, array $options = [], array $headers = []) {
     return $out;
   }
 
+  /**
+   * Retrieves a Drupal path or an absolute path and JSON decodes the result.
+   *
+   * @param \Drupal\Core\Url|string $path
+   *   Drupal path or URL to request AJAX from.
+   * @param array $options
+   *   Array of URL options.
+   * @param array $headers
+   *   Array of headers. Eg array('Accept: application/vnd.drupal-ajax').
+   *
+   * @return array
+   *   Decoded json.
+   */
+  protected function drupalGetJSON($path, array $options = [], array $headers = []) {
+    return Json::decode($this->drupalGetWithFormat($path, 'json', $options, $headers));
+  }
+
+  /**
+   * Retrieves a Drupal path or an absolute path for a given format.
+   *
+   * @param \Drupal\Core\Url|string $path
+   *   Drupal path or URL to request given format from.
+   * @param string $format
+   *   The wanted request format.
+   * @param array $options
+   *   Array of URL options.
+   * @param array $headers
+   *   Array of headers.
+   *
+   * @return mixed
+   *   The result of the request.
+   */
+  protected function drupalGetWithFormat($path, $format, array $options = [], array $headers = []) {
+    $options += ['query' => ['_format' => $format]];
+    return $this->drupalGet($path, $options, $headers);
+  }
+
   /**
    * Takes a path and returns an absolute path.
    *