diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/debug/Object-preventExtensions-01.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/debug/Object-preventExtensions-01.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,17 @@
+// Basic preventExtensions test.
+
+var g = newGlobal();
+var obj = g.eval("({x: 1})");
+assertEq(g.Object.isExtensible(obj), true);
+
+var dbg = new Debugger;
+var gw = dbg.addDebuggee(g);
+var objw = gw.makeDebuggeeValue(obj);
+assertEq(objw.isExtensible(), true);
+
+assertEq(objw.preventExtensions(), undefined);
+assertEq(g.Object.isExtensible(obj), false);
+assertEq(objw.isExtensible(), false);
+
+// Calling preventExtensions again has no effect.
+assertEq(objw.preventExtensions(), undefined);