diff -r 000000000000 -r 6474c204b198 js/src/tests/ecma_5/extensions/watch-setter-become-setter.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/tests/ecma_5/extensions/watch-setter-become-setter.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,44 @@
+/*
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/licenses/publicdomain/
+ */
+
+/* Create an object with a JavaScript setter. */
+var firstSetterCount;
+var o = { w:2, set x(v) { firstSetterCount++; } };
+
+/*
+ * Put the object in dictionary mode, so that JSObject::putProperty will 
+ * mutate its shapes instead of creating new ones.
+ */
+delete o.w;
+
+/* A stock watcher function. */
+var watcherCount;
+function watcher(id, oldval, newval) { watcherCount++; return newval; }
+
+/*
+ * Place a watchpoint on the property. The property's shape now has the
+ * watchpoint setter, with the original setter saved in the watchpoint
+ * structure.
+ */
+o.watch('x', watcher);
+
+/*
+ * Replace the setter with a new setter. The shape should get updated to
+ * refer to the new setter, and then the watchpoint setter should be
+ * re-established.
+ */
+var secondSetterCount;
+Object.defineProperty(o, 'x', { set: function () { secondSetterCount++ } });
+
+/*
+ * Assign to the property. This should trigger the watchpoint and the new setter.
+ */
+watcherCount = firstSetterCount = secondSetterCount = 0;
+o.x = 3;
+assertEq(watcherCount, 1);
+assertEq(firstSetterCount, 0);
+assertEq(secondSetterCount, 1);
+
+reportCompare(true, true);