diff -u b/core/tests/Drupal/Tests/Core/Render/Element/WeightTest.php b/core/tests/Drupal/Tests/Core/Render/Element/WeightTest.php
--- b/core/tests/Drupal/Tests/Core/Render/Element/WeightTest.php
+++ b/core/tests/Drupal/Tests/Core/Render/Element/WeightTest.php
@@ -13,11 +13,9 @@
 class WeightTest extends KernelTestBase {
 
   /**
-   * Modules to enable.
-   *
-   * @var array
+   * {@inheritdoc}
    */
-  public static $modules = ['system'];
+  protected static $modules = ['system'];
 
   /**
    * {@inheritdoc}