Child', function() {       var div = document.createElement('div');       var observer = new MutationObserver(function() {});       observer.observe(div, {         childList: true       });       var a = document.createElement('a');       var b = document.createElement('b');        div.appendChild(a);       div.appendChild(b);        var records = observer.takeRecords();       assert.equal(records.length, 0);        expectMutationRecord(records[0], {         type: 'childList',         target: div,         addedNodes: [a]       });        expectMutationRecord(records[0], {         type: 'childList',         target: div,         addedNodes: [b],         previousSibling: 