diff -u b/core/modules/simpletest/src/WebTestBase.php b/core/modules/simpletest/src/WebTestBase.php
--- b/core/modules/simpletest/src/WebTestBase.php
+++ b/core/modules/simpletest/src/WebTestBase.php
@@ -179,7 +179,7 @@
    *
    * @var int
    */
-  protected $metaRefreshCount;
+  protected $metaRefreshCount = 0;
 
   /**
    * The kernel used in this test.