anchor.diff:  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';
  
positive.code:       futureOrType.element,
        streamType.element
      ];
      asyncUnit.source = new TestSource('dart:async');
      asyncUnit.librarySource = asyncUnit.source;
      LibraryElementImpl coreLibrary = new LibraryElementImpl.forNode(
          null, null, AstTestFactory.libraryIdentifier2(["dart.core"]), true);
  
negative.code:       symbolType.element,
        typeType.element
      ];
      coreUnit.source = new StringSource('', null, uri: Uri.parse('dart:core'));
      coreUnit.librarySource = coreUnit.source;
      CompilationUnitElementImpl asyncUnit = new CompilationUnitElementImpl();
      asyncUnit.types = <ClassElement>[
  