.removeChild(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,         nextSibling: a,         addedNodes: [b]       });        expectMutationRecord(records[0], {         type: 'childList',         target: div,         nextSibling: a,         removedNodes: [b]       });     });      test('subtree', function() {       var div = document.createElement('div');       var child = div.appendChild(document.createElement('div'));       var observer = new MutationObserver(function() {});       observer.observe(child, {         childList: true       });       var a = document.createTextNode('a');       var b = document.createTextNode('b');        child.appendChild(a);       