anchor.diff:  // 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';
  
positive.code:       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 {
    final Map<AssetId, String> assets;
    final parsedUnits = <AssetId>{};
    final resolvedLibs = <AssetId>{};
  
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';
  