diff -u b/modules/simpletest/tests/file.test b/modules/simpletest/tests/file.test
--- b/modules/simpletest/tests/file.test
+++ b/modules/simpletest/tests/file.test
@@ -1004,7 +1004,7 @@
       $this->fail('Expected exception not thrown');
     }
     catch (RuntimeException $e) {
-      $this->assertEqual("Invalid filename 'a\xFFtest\x80€.txt'", $e->getMessage());
+      $this->assertEqual("Invalid filename 'a\xFFtest\x80€.txt'", $e->getMessage(), 'Invalid destination has been detected and RuntimeException has been thrown');
     }
   }