anchor.diff:  
     group('register', () {
       test('register', () {
  -      document.register('x-type1', CustomType);
  +      var tag = nextTag;
  +      document.register(tag, CustomType);
   
  -      var element = new Element.tag('x-type1');
  +      var element = new Element.tag(tag);
         expect(element, isNotNull);
         expect(element is CustomType, isTrue);
         expect(element.onCreatedCalled, isTrue);
       });
   
       test('register twice', () {
  -      document.register('x-type2', CustomType);
  +      var tag = nextTag;
  +      document.register(tag, CustomType);
         expect(() {
  -        document.register('x-type2', CustomType);
  +        document.register(tag, CustomType);
         }, throws, reason: 'Cannot register a tag more than once.');
   
  -      document.register('x-type3', CustomType);
  +      var newTag = nextTag;
  +      document.register(newTag, CustomType);
   
  -      var element = new Element.tag('x-type3');
  +      var element = new Element.tag(newTag);
         expect(element, isNotNull);
         expect(element is CustomType, isTrue);
       });
   
       test('register null', () {
         expect(() {
  -        document.register('x-type4', null);
  +        document.register(nextTag, null);
         }, throws, reason: 'Cannot register a null type.');
       });
   
       test('register native', () {
         expect(() {
  -        document.register('x-type5', BodyElement);
  +        document.register(nextTag, BodyElement);
         }, throws, reason: 'Cannot register a native element.');
       });
   
       test('register non-element', () {
         expect(() {
  -        document.register('x-type6', NotAnElement);
  +        document.register(nextTag, NotAnElement);
         }, throws, reason: 'Cannot register a non-element.');
       });
     });
  
positive.code: import '../../pkg/unittest/lib/html_individual_config.dart';
  import 'dart:html';
  
  class CustomType extends HtmlElement {
    factory CustomType() => null;
    bool onCreatedCalled; // = false;
    void onCreated() {
      onCreatedCalled = true;
      customCreatedCount++;
    }
  }
  
  int customCreatedCount = 0;
  
  class NotAnElement {}
  
  
negative.code:         firedOnPre = true;
        });
  
        document.register(tag, CustomType);
  
        var postElement = dom.children[0];
        expect(postElement, isNotNull);
  