diff --git a/core/modules/simpletest/src/WebTestBase.php b/core/modules/simpletest/src/WebTestBase.php
index c890beb..d0de644 100644
--- a/core/modules/simpletest/src/WebTestBase.php
+++ b/core/modules/simpletest/src/WebTestBase.php
@@ -1548,6 +1548,10 @@ protected function drupalGet($path, array $options = array(), array $headers = a
     $verbose .= '<hr />' . $out;
 
     $this->verbose($verbose);
+
+    $this->assertNoText(Html::escape('<'));
+    $this->assertNoText(Html::escape('</'));
+
     return $out;
   }
 
@@ -1781,6 +1785,9 @@ protected function drupalPostForm($path, $edit, $submit, array $options = array(
           $verbose .= '<hr />' . $out;
 
           $this->verbose($verbose);
+
+          $this->assertNoText(Html::escape('<'));
+          $this->assertNoText(Html::escape('</'));
           return $out;
         }
       }