diff -r 000000000000 -r 6474c204b198 js/xpconnect/tests/unit/test_bug1021312.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/xpconnect/tests/unit/test_bug1021312.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,16 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+const Cu = Components.utils;
+function run_test() {
+  let sb = new Cu.Sandbox(this);
+  var called = false;
+
+  Cu.exportFunction(function(str) { do_check_true(/someString/.test(str)); called = true; },
+                    sb, { defineAs: "func" });
+  // Do something weird with the string to make sure that it doesn't get interned.
+  Cu.evalInSandbox("var str = 'someString'; for (var i = 0; i < 10; ++i) str += i;", sb);
+  Cu.evalInSandbox("func(str);", sb);
+  do_check_true(called);
+}