michael@0: load(libdir + "asserts.js");
michael@0: 
michael@0: // Throw a TypeError if the trap reports the same property twice
michael@0: assertThrowsInstanceOf(function () {
michael@0:     Object.getOwnPropertyNames(new Proxy({}, {
michael@0:         getOwnPropertyNames: function (target) {
michael@0:             return [ 'foo', 'foo' ];
michael@0:         }
michael@0:     }));
michael@0: }, TypeError);