diff --git a/core/modules/image/src/Tests/ImageFieldTestBase.php b/core/modules/image/src/Tests/ImageFieldTestBase.php
index c023917e36..6ac64b81ec 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/ImageAdminStylesTest.php b/core/modules/image/tests/src/Functional/ImageAdminStylesTest.php
similarity index 99%
rename from core/modules/image/src/Tests/ImageAdminStylesTest.php
rename to core/modules/image/tests/src/Functional/ImageAdminStylesTest.php
index 5313b7fdbb..fa2c2f8081 100644
--- a/core/modules/image/src/Tests/ImageAdminStylesTest.php
+++ b/core/modules/image/tests/src/Functional/ImageAdminStylesTest.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\image\Tests;
+namespace Drupal\Tests\image\Functional;
 
 use Drupal\Component\Utility\SafeMarkup;
 use Drupal\Core\Entity\Entity\EntityViewDisplay;
@@ -8,6 +8,7 @@
 use Drupal\image\ImageStyleInterface;
 use Drupal\node\Entity\Node;
 use Drupal\file\Entity\File;
+use Drupal\Tests\TestFileCreationTrait;
 
 /**
  * Tests creation, deletion, and editing of image styles and effects.
@@ -16,6 +17,11 @@
  */
 class ImageAdminStylesTest extends ImageFieldTestBase {
 
+  use TestFileCreationTrait {
+    getTestFiles as drupalGetTestFiles;
+    compareFiles as drupalCompareFiles;
+  }
+
   /**
    * Given an image style, generate an image.
    */
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 b3e100dd9f..6c22760c3e 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 97%
rename from core/modules/image/src/Tests/ImageFieldDefaultImagesTest.php
rename to core/modules/image/tests/src/Functional/ImageFieldDefaultImagesTest.php
index d04a1c4d70..35f2056f29 100644
--- a/core/modules/image/src/Tests/ImageFieldDefaultImagesTest.php
+++ b/core/modules/image/tests/src/Functional/ImageFieldDefaultImagesTest.php
@@ -1,11 +1,13 @@
 <?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 field.
@@ -14,6 +16,14 @@
  */
 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 97%
rename from core/modules/image/src/Tests/ImageFieldDisplayTest.php
rename to core/modules/image/tests/src/Functional/ImageFieldDisplayTest.php
index 8061526da2..41ad68e177 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
@@ -258,6 +266,7 @@ public function testImageFieldSettings() {
 
     $nid = $this->uploadNodeImage($test_image, $field_name, 'article', $alt);
     $this->drupalGet('node/' . $nid . '/edit');
+    // TODO: result is not "" as expected.
     $this->assertFieldByName($field_name . '[0][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'
@@ -324,7 +333,7 @@ public function testImageFieldSettings() {
     $edit = [
       'files[' . $field_name . '_2][]' => drupal_realpath($test_image->uri),
     ];
-    $this->drupalPostAjaxForm(NULL, $edit, $field_name . '_2_upload_button');
+    $this->drupalPostForm(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">');
   }
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 e1f70d78a9..68ed0e2856 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 97%
rename from core/modules/image/src/Tests/ImageStylesPathAndUrlTest.php
rename to core/modules/image/tests/src/Functional/ImageStylesPathAndUrlTest.php
index 44254c6141..05164e8623 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.
diff --git a/core/modules/image/src/Tests/ImageThemeFunctionTest.php b/core/modules/image/tests/src/Functional/ImageThemeFunctionTest.php
similarity index 96%
rename from core/modules/image/src/Tests/ImageThemeFunctionTest.php
rename to core/modules/image/tests/src/Functional/ImageThemeFunctionTest.php
index 54c5c64a19..45a7636fb6 100644
--- a/core/modules/image/src/Tests/ImageThemeFunctionTest.php
+++ b/core/modules/image/tests/src/Functional/ImageThemeFunctionTest.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\image\Tests;
+namespace Drupal\Tests\image\Functional;
 
 use Drupal\Core\Field\FieldStorageDefinitionInterface;
 use Drupal\Core\Url;
@@ -8,15 +8,21 @@
 use Drupal\field\Entity\FieldConfig;
 use Drupal\file\Entity\File;
 use Drupal\image\Entity\ImageStyle;
-use Drupal\simpletest\WebTestBase;
 use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\Tests\BrowserTestBase;
+use Drupal\Tests\TestFileCreationTrait;
 
 /**
  * Tests image theme functions.
  *
  * @group image
  */
-class ImageThemeFunctionTest extends WebTestBase {
+class ImageThemeFunctionTest extends BrowserTestBase {
+
+  use TestFileCreationTrait {
+    getTestFiles as drupalGetTestFiles;
+    compareFiles as drupalCompareFiles;
+  }
 
   /**
    * Modules to enable.
diff --git a/core/modules/image/src/Tests/QuickEditImageControllerTest.php b/core/modules/image/tests/src/Functional/QuickEditImageControllerTest.php
similarity index 92%
rename from core/modules/image/src/Tests/QuickEditImageControllerTest.php
rename to core/modules/image/tests/src/Functional/QuickEditImageControllerTest.php
index 870c1bb5d5..aecc7346cc 100644
--- a/core/modules/image/src/Tests/QuickEditImageControllerTest.php
+++ b/core/modules/image/tests/src/Functional/QuickEditImageControllerTest.php
@@ -1,16 +1,16 @@
 <?php
 
-namespace Drupal\image\Tests;
+namespace Drupal\Tests\image\Functional;
 
+use Drupal\Tests\BrowserTestBase;
 use Drupal\Tests\image\Kernel\ImageFieldCreationTrait;
-use Drupal\simpletest\WebTestBase;
 
 /**
  * Tests the endpoints used by the "image" in-place editor.
  *
  * @group image
  */
-class QuickEditImageControllerTest extends WebTestBase {
+class QuickEditImageControllerTest extends BrowserTestBase {
 
   use ImageFieldCreationTrait;
 
@@ -77,8 +77,12 @@ 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());
+
   }
 
   /**
diff --git a/core/tests/Drupal/Tests/BrowserTestBase.php b/core/tests/Drupal/Tests/BrowserTestBase.php
index bd50c23b48..b8ea85eaec 100644
--- a/core/tests/Drupal/Tests/BrowserTestBase.php
+++ b/core/tests/Drupal/Tests/BrowserTestBase.php
@@ -673,6 +673,43 @@ protected function drupalGet($path, array $options = [], array $headers = []) {
   }
 
   /**
+   * 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.
    *
    * @param string $path