diff -u b/core/modules/system/lib/Drupal/system/Tests/Upgrade/FieldUpgradePathTest.php b/core/modules/system/lib/Drupal/system/Tests/Upgrade/FieldUpgradePathTest.php
--- b/core/modules/system/lib/Drupal/system/Tests/Upgrade/FieldUpgradePathTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Upgrade/FieldUpgradePathTest.php
@@ -196,7 +196,7 @@
     $this->assertEqual($body->format, 'filtered_html');
 
     // Check that creation of a new node works as expected.
-    $value = $this->randomString(20);
+    $value = $this->randomName();
     $edit = array(
       'title' => 'Node after CMI conversion',
       'body[und][0][value]' => $value,