diff --git a/core/modules/system/tests/modules/ajax_test/src/Controller/AjaxTestController.php b/core/modules/system/tests/modules/ajax_test/src/Controller/AjaxTestController.php
index 9f10db4..b815be3 100644
--- a/core/modules/system/tests/modules/ajax_test/src/Controller/AjaxTestController.php
+++ b/core/modules/system/tests/modules/ajax_test/src/Controller/AjaxTestController.php
@@ -6,7 +6,6 @@
 use Drupal\Core\Ajax\AlertCommand;
 use Drupal\Core\Ajax\CloseDialogCommand;
 use Drupal\Core\Ajax\HtmlCommand;
-use Drupal\Core\EventSubscriber\MainContentViewSubscriber;
 use Drupal\Core\Url;
 use Symfony\Component\HttpFoundation\Request;
 
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxThemeTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxThemeTest.php
index c7b125b..565fbb7 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxThemeTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxThemeTest.php
@@ -2,14 +2,14 @@
 
 namespace Drupal\FunctionalJavascriptTests\Ajax;
 
-use Drupal\Tests\BrowserTestBase;
+use Drupal\FunctionalJavascriptTests\JavascriptTestBase;
 
 /**
- * Ensures that ajax themes are rendered in the frontend theme.
+ * Tests that AJAX responses use the current theme.
  *
  * @group Ajax
  */
-class AjaxThemeTest extends BrowserTestBase {
+class AjaxThemeTest extends JavascriptTestBase {
 
   /**
    * {@inheritdoc}
@@ -17,9 +17,10 @@ class AjaxThemeTest extends BrowserTestBase {
   public static $modules = ['ajax_test'];
 
   public function testAjaxWithAdminRoute() {
-    \Drupal::service('theme_installer')->install(['seven']);
+    \Drupal::service('theme_installer')->install(['stable', 'seven']);
     $theme_config = \Drupal::configFactory()->getEditable('system.theme');
     $theme_config->set('admin', 'seven');
+    $theme_config->set('default', 'stable');
     $theme_config->save();
 
     $account = $this->drupalCreateUser(['view the administration theme']);
@@ -27,19 +28,28 @@ public function testAjaxWithAdminRoute() {
 
     // First visit the site directly via the URL. This should render it in the
     // admin theme.
-    $this->drupalGet('/admin/ajax-test/theme');
+    $this->drupalGet('admin/ajax-test/theme');
     $assert = $this->assertSession();
     $assert->pageTextContains('Current theme: seven');
 
     // Now
-    $this->drupalGet('/ajax-test/dialog');
+    $this->drupalGet('ajax-test/dialog');
     $assert->pageTextNotContains('Current theme: stable');
     $this->clickLink('Link 8 (ajax)');
+    $this->waitForAjaxToFinish();
+    file_put_contents('/tmp/foo.png', $this->getSession()->getScreenshot());
+    file_put_contents('/tmp/foo.html', $this->getSession()->getPage()->getHtml());
 
     $assert->pageTextContains('Current theme: stable');
     $assert->pageTextNotContains('Current theme: seven');
-    $this->clickLink('Link 8 (ajax)');
   }
-  
+
+  /**
+   * Waits for jQuery to become active and animations to complete.
+   */
+  protected function waitForAjaxToFinish() {
+    $condition = "(0 === jQuery.active && 0 === jQuery(':animated').length)";
+    $this->assertJsCondition($condition, 10000);
+  }
 
 }