diff -u b/core/modules/system/src/Tests/Cache/CacheContextOptimizationTest.php b/core/modules/system/src/Tests/Cache/CacheContextOptimizationTest.php
--- b/core/modules/system/src/Tests/Cache/CacheContextOptimizationTest.php
+++ b/core/modules/system/src/Tests/Cache/CacheContextOptimizationTest.php
@@ -81,11 +81,11 @@
   }
 
   /**
-   * Ensures that 'user.roles' cache context is defining cacheable metadata.
+   * Ensures that 'user.roles' still works when it is optimized away.
    */
   public function testUserRolesCacheContextOptimization() {
-    $user1 = $this->createUser();
-    $this->assertEqual($user1->id(), 1);
+    $root_user = $this->createUser();
+    $this->assertEqual($root_user->id(), 1);
 
     $authenticated_user = $this->createUser(['administer permissions']);
     $role = $authenticated_user->getRoles()[1];
@@ -110,10 +110,9 @@
     $this->assertEqual($output, 'content for authenticated users');
 
     // Even though the cache contexts have been optimized to only include 'user'
-    // cache context, the element should have been changed because
-    // 'user.roles' cache context defined a cacheable metadata for permission
-    // changes, which should have bubbled up for the element when it was
-    // optimized away.
+    // cache context, the element should have been changed because 'user.roles'
+    // cache context defined a cache tag for user entity changes23, which should
+    // have bubbled up for the element when it was optimized away.
     $authenticated_user->removeRole($role);
     $authenticated_user->save();
     $element = $test_element;
@@ -123,2 +122,3 @@
   }
+
 }