anchor.diff:  
     LibraryElementInBuildUnit get testLibrary;
   
  -  /// Add the given package bundle as a dependency so that it may be referenced
  -  /// by the files under test.
  -  void addBundle(String path, PackageBundle bundle);
  -
     void createLinker(String text, {String path: '/test.dart'});
  -
  -  /// Link together the given file, along with any other files passed to
  -  /// [addNamedSource], to form a package bundle.  Reset the state of the
  -  /// buffers accumulated by [addNamedSource] and [addBundle] so that further
  -  /// bundles can be created.
  -  PackageBundleBuilder createPackageBundle(String text,
  -      {String path: '/test.dart', String uri});
   }
   
   /// Implementation of [SummaryLinkerTestStrategy] that drives summary generation
  
positive.code: 
    @override
    bool get _allowMissingFiles => false;
  
    @override
    void addBundle(String path, PackageBundle bundle) {
      _filesToLink.summaryDataStore.addBundle(path, bundle);
    }
  
    @override
    void createLinker(String text, {String path: '/test.dart'}) {
  
negative.code:       assembler.addUnlinkedUnitViaUri(uri, unit);
      });
      return assembler.assemble();
    }
  
    UnlinkedUnitBuilder createUnlinkedSummary(Uri uri, String text) =>
  