diff --git a/tests/UnusedCodeTest.php b/tests/UnusedCodeTest.php
index 7e89aa808..a740af917 100644
--- a/tests/UnusedCodeTest.php
+++ b/tests/UnusedCodeTest.php
@@ -670,6 +670,10 @@ class UnusedCodeTest extends TestCase
                         public function current() {
                             return $this->current;
                         }
+
+                        public function key() {
+                            return 5;
+                        }
                     }
 
                     $items = new IterableResult();