anchor.diff:        throw UnimplementedError();
   }
   
  -class _TestingBuildStep implements BuildStep {
  -  @override
  -  final AssetId inputId;
  -
  -  @override
  -  final _TestingResolver resolver;
  -
  -  final Map<AssetId, String> assets;
  -
  -  _TestingBuildStep(this.inputId, this.assets)
  -      : resolver = _TestingResolver(assets);
  -
  -  @override
  -  Future<bool> canRead(AssetId id) async => assets.containsKey(id);
  -
  -  @override
  -  Future<String> readAsString(AssetId id, {Encoding encoding = utf8}) async =>
  -      assets[id]!;
  -
  -  @override
  -  void noSuchMethod(_) => throw UnimplementedError();
  -}
  -
  -class _TestingResolver implements Resolver {
  +class _TestingResolver implements ReleasableResolver {
     final Map<AssetId, String> assets;
     final parsedUnits = <AssetId>{};
     final resolvedLibs = <AssetId>{};
  
positive.code: // BSD-style license that can be found in the LICENSE file.
  
  @TestOn('vm')
  import 'dart:convert';
  
  import 'package:analyzer/dart/analysis/utilities.dart';
  import 'package:analyzer/dart/ast/ast.dart';
  import 'package:analyzer/dart/element/element.dart';
  
negative.code:   }
  
    @override
    void release() {}
  
    @override
    void noSuchMethod(_) => throw UnimplementedError();
  }
  
  class _FixedResolvers implements Resolvers {
    final ReleasableResolver _resolver;
  
    _FixedResolvers(this._resolver);
  
    @override
    Future<ReleasableResolver> get(BuildStep buildStep) =>
        Future.value(_resolver);
  
    @override
    void reset() {}
  }
  
  const _customHeader = '// Copyright 1979';
  