diff -r 000000000000 -r 6474c204b198 js/src/tests/js1_8_5/extensions/is-generator.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/tests/js1_8_5/extensions/is-generator.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,23 @@
+/*
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/licenses/publicdomain/
+ */
+
+/*
+ * Bug 648355: Function.prototype.isGenerator
+ */
+
+reportCompare(true, "isGenerator" in Function.prototype, "Function.prototype.isGenerator present");
+
+reportCompare(false, (function(){}).isGenerator(), "lambda is not a generator fn");
+reportCompare(false, Function.prototype.toString.isGenerator(), "native is not a generator fn");
+reportCompare(false, (function(){with(obj){}}).isGenerator(), "heavyweight is not a generator fn");
+reportCompare(false, (function(){obj}).isGenerator(), "upvar function is not a generator fn");
+
+reportCompare(true, (function(){yield}).isGenerator(), "simple generator fn");
+reportCompare(true, (function(){with(obj){yield}}).isGenerator(), "heavyweight generator fn");
+reportCompare(true, (function(){yield; obj}).isGenerator(), "upvar generator fn");
+
+reportCompare(false, Function.prototype.isGenerator.call(42), "number is not a generator fn");
+reportCompare(false, Function.prototype.isGenerator.call({}), "vanilla object is not a generator fn");
+reportCompare(false, Function.prototype.isGenerator.call(new Date()), "date object is not a generator fn");