diff -r 000000000000 -r 6474c204b198 js/xpconnect/tests/chrome/file_expandosharing.jsm
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/xpconnect/tests/chrome/file_expandosharing.jsm	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,10 @@
+this.EXPORTED_SYMBOLS = ['checkFromJSM'];
+
+this.checkFromJSM = function checkFromJSM(target, is_op) {
+  is_op(target.numProp, 42, "Number expando works");
+  is_op(target.strProp, "foo", "String expando works");
+  // If is_op is todo_is, target.objProp will be undefined.
+  try {
+    is_op(target.objProp.bar, "baz", "Object expando works");
+  } catch(e) { is_op(0, 1, "No object expando"); }
+}