Remove unnecessary coupling between Promise tests and Object.observe

test/promises-aplus/lib/mocha.js

Index: test/promises-aplus/lib/mocha.js
diff --git a/test/promises-aplus/lib/mocha.js b/test/promises-aplus/lib/mocha.js
index 24d294ef8f829889fbcdccf1a9893f92635c7aea..f09f11130b2c6a901715d757180de4ca478533be 100644
--- a/test/promises-aplus/lib/mocha.js
+++ b/test/promises-aplus/lib/mocha.js
@@ -42,12 +42,7 @@ var assert = require('assert');
 var TIMEOUT = 1000;
 
 function PostMicrotask(fn) {
-  var o = {};
-  Object.observe(o, function() {
-    fn();
-  });
-  // Change something to enqueue a microtask.
-  o.x = 'hello';
+  Promise.resolve().then(fn);
 }
 
 var context = {