diff --git a/core/modules/system/lib/Drupal/system/Tests/Entity/EntityUnitTestBase.php b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityUnitTestBase.php
index 9e6b987..0fed4c8 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Entity/EntityUnitTestBase.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Entity/EntityUnitTestBase.php
@@ -33,7 +33,9 @@ public function setUp() {
    * Creates a user.
    *
    * @param array $values
-   *   (optional) The values used to create the entity.
+   *   (optional) The values used to create the entity. To perform access checks
+   *   and prevent the new user from becoming uid 1 (which exempts from all user
+   *   access conditions), pass a unique value other than 1 as 'uid' in $values.
    *
    * @return \Drupal\user\Plugin\Core\Entity\User
    *   The created user entity.
@@ -42,9 +44,10 @@ protected function createUser($values = array()) {
     $account = entity_create('user', $values + array(
       'name' => $this->randomName(),
     ));
-    // Allow to create a new user entity with a specific user id, make sure it
-    // it will be saved as a new entity instead of trying to update the
-    // non-existing entity with that id.
+    // Force the entity to be new, so that callers are able to specify
+    // a 'uid' in $values to skip over uid 1. If no uid is provided explicitly,
+    // \Drupal\user\UserStorageController will automatically choose and insert
+    // the next available ID.
     $account->enforceIsNew();
     $account->save();
     return $account;