anchor.diff:    test('LastIndexOf', () {
       Element root = insertTestDiv();
   
  -    List<Element> someChecked = document.querySelector('#someChecked').children;
  -
  -    List<Element> noneChecked = document.querySelector('#noneChecked').children;
  +    List<Element> someChecked =
  +        document.querySelector('#someChecked')!.children;
  +
  +    List<Element> noneChecked =
  +        document.querySelector('#noneChecked')!.children;
   
       expect(someChecked.length, 4);
       expect(noneChecked.length, 4);
  
positive.code: // Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
  // for details. All rights reserved. Use of this source code is governed by a
  // BSD-style license that can be found in the LICENSE file.
  
  // @dart = 2.7
  
  import 'dart:html';
  
  
negative.code:   test('Every', () {
      Element root = insertTestDiv();
  
      List<Element> eachChecked = document.querySelector('#allChecked')!.children;
  
      List<Element> someChecked =
          document.querySelector('#someChecked')!.children;
  
      List<Element> noneChecked =
          document.querySelector('#noneChecked')!.children;
  
      expect(eachChecked.length, 4);
      expect(someChecked.length, 4);
  