The Tor Browser / file revision

 /* This Source Code Form is subject to the terms of the Mozilla Public

  * License, v. 2.0. If a copy of the MPL was not distributed with this

  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

 'use strict';

 const { PrefsTarget } = require('sdk/preferences/event-target');

 const { get, set, reset } = require('sdk/preferences/service');

 const { Loader } = require('sdk/test/loader');

 const { setTimeout } = require('sdk/timers');

 const root = PrefsTarget();

 exports.testPrefsTarget = function(assert, done) {

   let loader = Loader(module);

   let pt = loader.require('sdk/preferences/event-target').PrefsTarget({});

   let name = 'test';

   assert.equal(get(name, ''), '', 'test pref is blank');

   pt.once(name, function() {

     assert.equal(pt.prefs[name], 2, 'test pref is 2');

     pt.once(name, function() {

       assert.fail('should not have heard a pref change');

     });

     loader.unload();

     root.once(name, function() {

       assert.pass('test pref was changed');

       reset(name);

       // NOTE: using setTimeout to make sure that the other listener had

       //       a chance to fail

       // end test

       setTimeout(done);

     });

     set(name, 3);

   });

   pt.prefs[name] = 2;

 };

 require('sdk/test').run(exports);