test for complete property descriptor support

Author: mikesamuel

test/unit/es6/canary.js

@@ -2,6 +2,10 @@
 // older browsers.
 `I load on ES6`;
 
+if (!Object.getOwnPropertyDescriptors) {
+  throw new Error('Incomplete property descriptor support');
+}
+
 module.exports = function usesRestArgs (...args) {
   return args;
 };