michael@0: load(libdir + "asserts.js");
michael@0: 
michael@0: /*
michael@0:  * Throw a TypeError if both the current descriptor and the descriptor returned
michael@0:  * by the trap are data descriptors, the current descriptor is non-configurable
michael@0:  * and non-writable, and the descriptor returned by the trap is writable.
michael@0:  */
michael@0: var target = {};
michael@0: Object.defineProperty(target, 'foo', {
michael@0:     value: 'bar',
michael@0:     writable: false,
michael@0:     configurable: false
michael@0: });
michael@0: assertThrowsInstanceOf(function () { 
michael@0:     Object.getOwnPropertyDescriptor(new Proxy(target, {
michael@0:         getOwnPropertyDescriptor: function (target, name) {
michael@0:             return {
michael@0:                 value: 'bar',
michael@0:                 writable: true,
michael@0:                 configurable: false
michael@0:             };
michael@0:         }
michael@0:     }), 'foo');
michael@0: }, TypeError);