.removeChild(b);        var records = observer.takeRecords();       assert.equal(records.length, 0);        expectMutationRecord(records[0], {         type: 'childList',         target: child,         addedNodes: [a]       });        expectMutationRecord(records[0], {         type: 'childList',         target: child,         nextSibling: a,         addedNodes: [b]       });        expectMutationRecord(records[0], {         type: 'childList',         target: child,         nextSibling: a,         removedNodes: [b]       });     });      test('