michael@0: load(libdir + "asserts.js");
michael@0: 
michael@0: // Throw a TypeError if the object refuses to be made non-extensible
michael@0: assertThrowsInstanceOf(function () {
michael@0:     Object.preventExtensions(new Proxy({}, {
michael@0:         preventExtensions: function () {
michael@0:             return false;
michael@0:         }
michael@0:     }));
michael@0: }, TypeError);