nt', function() {       var div = document.createElement('div');       var a = div.appendChild(document.createTextNode('a'));        var observer = new MutationObserver(function() {});       observer.observe(div, {         childList: true       });        var df = document.createDocumentFragment();       var b = df.appendChild(document.createTextNode('b'));       var c = df.appendChild(document.createTextNode('c'));       var d = df.appendChild(document.createTextNode('d'));        div.insertBefore(df, a);        var records = observer.takeRecords();       assert.equal(records.length, 0);       expectMutationRecord(records[0], {         type: 'childList',         target: div,         addedNodes: makeNodeList(b, c, d),         removedNodes: makeNodeList(),         previousSibling: null,         nextSibling: 