在Dart中测试代码生成时出错：生成器未能写入资源

我已经创建了一个Dart（Dart v2）代码生成器来检测Cooper类型的注释

生成器如下所示：

class CooperGenerator extends GeneratorForAnnotation<Cooper> {
  @override
  Future<String> generateForAnnotatedElement(
      Element element, ConstantReader annotation, BuildStep buildStep) async {
    final name = annotation?.peek("implementationClassName")?.stringValue ?? "CooperApi";
    return "class $name {}";
  }
}

import 'package:build/build.dart';
import 'package:test/test.dart';
import 'package:build_test/build_test.dart';
import 'package:source_gen/source_gen.dart';
import 'package:cooper_generator/cooper_generator.dart';

void main() {
  group('CooperGenerator', () {
    test('generates implementation for classes annotated with @Cooper',
        () async {
      final builder = PartBuilder([CooperGenerator()], '.g.dart');
      await testBuilder(builder, _inputs, outputs: _output);
    });
  });
}

final _output = {
  "jorge|lib/coop.g.dart": '''
// GENERATED CODE - DO NOT MODIFY BY HAND

part of 'coop.dart';

// **************************************************************************
// CooperGenerator
// **************************************************************************

class CooperImplementation {}
          '''
};

final _inputs = <String, String>{
  'cooper|lib/cooper.dart': _cooperSource,
  'jorge|lib/coop.dart': _classToGenerate,
};

const String _classToGenerate = r'''
    import 'package:cooper/cooper.dart';
    @Cooper("CooperImplementation")
    abstract class CooperContract {}
''';

const String _cooperSource = r'''
class Cooper {
  final String implementationClassName;

  const Cooper(this.implementationClassName);
}
''';

类CooperGenerator扩展GeneratorForAnnotation{
@凌驾
未来生成ForNotatedElement(
元素元素，ConstantTreader注释，BuildStep（BuildStep）异步{
最终名称=注释？.peek（“implementationClassName”）？.stringValue？？？“CooperApi”；
返回“class$name{}”；
}
}

我正在编写单元测试，以验证我的生成器是否按预期工作。看起来像这样：

class CooperGenerator extends GeneratorForAnnotation<Cooper> {
  @override
  Future<String> generateForAnnotatedElement(
      Element element, ConstantReader annotation, BuildStep buildStep) async {
    final name = annotation?.peek("implementationClassName")?.stringValue ?? "CooperApi";
    return "class $name {}";
  }
}

import 'package:build/build.dart';
import 'package:test/test.dart';
import 'package:build_test/build_test.dart';
import 'package:source_gen/source_gen.dart';
import 'package:cooper_generator/cooper_generator.dart';

void main() {
  group('CooperGenerator', () {
    test('generates implementation for classes annotated with @Cooper',
        () async {
      final builder = PartBuilder([CooperGenerator()], '.g.dart');
      await testBuilder(builder, _inputs, outputs: _output);
    });
  });
}

final _output = {
  "jorge|lib/coop.g.dart": '''
// GENERATED CODE - DO NOT MODIFY BY HAND

part of 'coop.dart';

// **************************************************************************
// CooperGenerator
// **************************************************************************

class CooperImplementation {}
          '''
};

final _inputs = <String, String>{
  'cooper|lib/cooper.dart': _cooperSource,
  'jorge|lib/coop.dart': _classToGenerate,
};

const String _classToGenerate = r'''
    import 'package:cooper/cooper.dart';
    @Cooper("CooperImplementation")
    abstract class CooperContract {}
''';

const String _cooperSource = r'''
class Cooper {
  final String implementationClassName;

  const Cooper(this.implementationClassName);
}
''';

导入“包：build/build.dart”； 导入“包：test/test.dart”； 导入“包：build_test/build_test.dart”； 导入“包：源代码/源代码.省道”； 导入“包：库珀_生成器/cooper_生成器.dart”； void main（）{ 组（'CooperGenerator'，（）{ test（'为带@Cooper'注释的类生成实现， （）异步{ 最终生成器=零件生成器（[CooperGenerator（）]，“.g.dart”）； 等待testBuilder（生成器，_输入，输出：_输出）； }); }); } 最终输出={ “豪尔赫| lib/coop.g.dart”：” //生成的代码-不要手动修改 “鸡笼飞镖”的一部分； // ************************************************************************** //库珀发生器 // ************************************************************************** 类协同实现{} ''' }; 最终输入={ “cooper | lib/cooper.dart”：_cooperSource， “jorge | lib/coop.dart”：“类生成”， }; 常量字符串_classToGenerate=r'' 导入“包：cooper/cooper.dart”； @库珀（“合作实施”） 抽象类CooperContract{} '''; 常量字符串_cooperSource=r'' 库珀班{ 最终字符串实现classname； const Cooper（this.implementationClassName）； } '''; 代码运行得非常好，它生成了我期望的代码。但是，在运行单元测试时，我遇到了以下错误，我无法理解原因：

ERROR: Expected: contains AssetId:<jorge|lib/coop.g.dart>
Actual: ?:[]
Builder failed to write asset jorge|lib/coop.g.dart

package:test                                    expect
package:build_test/src/test_builder.dart 49:7   checkOutputs.<fn>
dart:collection                                 __InternalLinkedHashMap&_HashVMBase&MapMixin&_LinkedHashMapMixin.forEach
package:build_test/src/test_builder.dart 41:13  checkOutputs
package:build_test/src/test_builder.dart 140:3  testBuilder
===== asynchronous gap ===========================
dart:async                                      _AsyncAwaitCompleter.completeError
package:build_test/src/test_builder.dart        testBuilder
===== asynchronous gap ===========================
dart:async                                      _asyncThenWrapperHelper
package:build_test/src/test_builder.dart        testBuilder
test/generator_test.dart 12:13                  main.<fn>.<fn>

错误：应为：包含AssetId:
实际：？：[]
生成器未能写入资产jorge | lib/coop.g.dart
包：测试预期
包：build\u test/src/test\u builder.dart 49:7检查输出。
dart:collection\u InternalLinkedHashMap和\u HashVMBase&MapMixin和\u LinkedHashMapMixin.forEach
包：build\u test/src/test\u builder.dart 41:13检查输出
包：build\u test/src/test\u builder.dart 140:3 testBuilder
======异步间隙===========================
dart:async\u AsyncAwaitCompleter.completeError
包：build\u test/src/test\u builder.dart testBuilder
======异步间隙===========================
dart:async\u asyncThenWrapperHelper
包：build\u test/src/test\u builder.dart testBuilder
试验/发电机试验。dart 12:13主。。

有人知道为什么这会给我这个错误吗