The Tor Browser / file revision

 'use strict';

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

 const tabs = require('sdk/tabs');

 let closeEvents = 0;

 const closeEventDetector = _ => closeEvents++;

 exports.testNoTabCloseOnStartup = function(assert, done) {

   setTimeout(_ => {

     assert.equal(closeEvents, 0, 'there were no tab close events detected');

     tabs.open({

       url: 'about:mozilla',

       inBackground: true,

       onReady: tab => tab.close(),

       onClose: _ => {

         assert.equal(closeEvents, 1, 'there was one tab close event detected');

         done();

       }

     })

   });

 }

 exports.main = function() {

   tabs.on('close', closeEventDetector);

   require("sdk/test/runner").runTestsFromModule(module);

 }