diff -u b/core/modules/system/tests/src/Functional/Ajax/FrameworkTest.php b/core/modules/system/tests/src/Functional/Ajax/FrameworkTest.php
--- b/core/modules/system/tests/src/Functional/Ajax/FrameworkTest.php
+++ b/core/modules/system/tests/src/Functional/Ajax/FrameworkTest.php
@@ -3,7 +3,6 @@
 namespace Drupal\Tests\system\Functional\Ajax;
 
 use Drupal\Component\Serialization\Json;
-use Drupal\Core\Ajax\AddCssCommand;
 use Drupal\Core\Ajax\AlertCommand;
 use Drupal\Core\Ajax\AppendCommand;
 use Drupal\Core\Ajax\HtmlCommand;
only in patch2:
unchanged:
--- a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/CommandsTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/CommandsTest.php
@@ -33,10 +33,6 @@ public function testAjaxCommands() {
     $this->drupalLogin($web_user);
     $this->drupalGet($form_path);
 
-    // Tests the 'add_css' command.
-    $page->pressButton("AJAX 'add_css' command");
-    $this->assertWaitPageContains('my/file.css');
-
     // Tests the 'after' command.
     $page->pressButton("AJAX 'After': Click to put something after the div");
     $this->assertWaitPageContains('<div id="after_div">Something can be inserted after this</div>This will be placed after');
@@ -140,6 +136,19 @@ public function testAjaxCommands() {
     $this->assertWaitPageContains('<div class="test-settings-command">42</div>');
   }
 
+  /**
+   * Tests the deprecated Ajax Commands.
+   *
+   * @group legacy
+   */
+  public function testDeprecatedAjaxCommands() {
+    $page = $this->getSession()->getPage();
+
+    // Tests the 'add_css' command.
+    $page->pressButton("AJAX 'add_css' command");
+    $this->assertWaitPageContains('my/file.css');
+  }
+
   /**
    * Asserts that page contains a text after waiting.
    *