anchor.diff:  
   /// Generates data based on random seed, without any network (or file) access.
   class _AutoGeneratedImportSource implements ImportSource {
  +  final _archives = <String, List<int>>{};
  +
     @override
     Future<List<ResolvedVersion>> resolveVersions(TestProfile profile) async {
       final versions = <ResolvedVersion>[];
  
positive.code: 
  import 'models.dart';
  import 'resolver.dart' as resolver;
  
  /// Interface for resolving and getting data for profiles.
  abstract class ImportSource {
  
negative.code: 
    @override
    Future<List<int>> getArchiveBytes(String package, String version) async {
      return _archives.putIfAbsent('$package/$version', () {
        final archive = ArchiveBuilder();
  
        final isFlutter = package.startsWith('flutter_');
        final pubspec = json.encode({
          'name': package,
          'version': version,
          'environment': {
            'sdk': '>=2.6.0 <3.0.0',
          },
          'dependencies': {
            if (isFlutter) 'flutter': {'sdk': 'flutter'},
          },
        });
        archive.addFile('pubspec.yaml', pubspec);
        archive.addFile('README.md', '# $package\n\nAwesome package.');
        archive.addFile('CHANGELOG.md', '## $version\n\n- updated');
        archive.addFile(
            'lib/$package.dart', 'main() {\n  print(\'Hello.\');\n}\n');
        archive.addFile(
            'example/example.dart', 'main() {\n  print(\'example\');\n}\n');
        archive.addFile('LICENSE', 'All rights reserved.');
        return archive.toTarGzBytes();
      });
    }
  
    @override
  