anchor.diff:        futureOrType.element,
         streamType.element
       ];
  -    asyncUnit.source = new TestSource('dart:async');
  +
  +    asyncUnit.source = new StringSource('', null, uri: Uri.parse('dart:async'));
       asyncUnit.librarySource = asyncUnit.source;
       LibraryElementImpl coreLibrary = new LibraryElementImpl.forNode(
           null, null, AstTestFactory.libraryIdentifier2(["dart.core"]), true);
  
positive.code:       symbolType.element,
        typeType.element
      ];
      coreUnit.source = new TestSource('dart:core');
      coreUnit.librarySource = coreUnit.source;
      CompilationUnitElementImpl asyncUnit = new CompilationUnitElementImpl();
      asyncUnit.types = <ClassElement>[
  
negative.code: import 'package:analyzer/src/generated/testing/element_factory.dart';
  import 'package:analyzer/src/generated/testing/test_type_provider.dart';
  import 'package:analyzer/src/source/source_resource.dart';
  import 'package:analyzer/src/string_source.dart';
  import 'package:analyzer/src/test_utilities/resource_provider_mixin.dart';
  import 'package:test/test.dart';
  import 'package:test_reflective_loader/test_reflective_loader.dart';
  