diff -u b/core/modules/system/src/Tests/Form/FormCacheTest.php b/core/modules/system/src/Tests/Form/FormCacheTest.php
--- b/core/modules/system/src/Tests/Form/FormCacheTest.php
+++ b/core/modules/system/src/Tests/Form/FormCacheTest.php
@@ -89,8 +89,7 @@
    * Tests the form cache without a logged-in user.
    */
   function testNoCacheToken() {
-    $current_user = $this->container->get('current_user');
-    $current_user->setAccount(new AnonymousUserSession());
+    \Drupal::service('account_switcher')->switchTo(new AnonymousUserSession());
 
     $this->form_state->set('example', $this->randomMachineName());
     \Drupal::formBuilder()->setCache($this->form_build_id, $this->form, $this->form_state);