Index: api/testing/case/functional.php
===================================================================
--- api/testing/case/functional.php	(revision 10921)
+++ api/testing/case/functional.php	(working copy)
@@ -133,7 +133,19 @@
     protected function loadResponse() {
         $response = api_response::getInstance();
         $resp = $response->getContents();
-        $this->responseDom = DOMDocument::loadXML($resp);
+
+        if (empty($resp)) {
+            throw new api_testing_exception("Empty response document");
+        }
+
+        $dom = new DOMDocument();
+        if (!$dom->loadXML($resp)) {
+            throw new api_testing_exception(
+                sprintf("Unable to load XML: '%s'", $resp));
+        }
+
+        $this->responseDom = $dom;
     }

     /**