单元测试Firestore相关方法时遇PlatformException问题求助

问题场景 #

在对调用Firestore的loadMedias方法进行单元测试时，触发以下错误：

PlatformException(channel-error, Unable to establish connection on channel., null, null)

相关代码 #

待测试方法：

Future<MediasState> loadMedias(AbstractEvent event) async {
    late AbstractBlocState streamState;
    try {
      DataHelper _dataHelperMediasEvent = DataHelperFactory.instance
          .createInstanceFromAnotherDataHelperAndEntityInstance(
              _dataHelperEvents, event, 'medias');
      List<AbstractMedia> medias =
          (await _dataHelperMediasEvent.getAll()).cast<AbstractMedia>();
      for (AbstractMedia media in medias) {
        media.user = await (_dataHelperUsers.getEntity(media.user.get()));
      }
      medias = sortEntitiesByCreatedDateDesc(medias) as List<AbstractMedia>;
      streamState = MediasShowed(medias);
    } catch (error) {
      streamState = MediasShowedError();
    } finally {
      return streamState as MediasState;
    }
  }

测试代码：

test('Test load medias', () async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
    AbstractEvent event =
        EntityFactory.createInstance('Event') as AbstractEvent;

    AbstractMedia media1 =
        EntityFactory.createInstance('Media') as AbstractMedia;

    AbstractMedia media2 =
        EntityFactory.createInstance('Media') as AbstractMedia;

    AbstractMedia media3 =
        EntityFactory.createInstance('Media') as AbstractMedia;

    List<AbstractMedia> listOfMedias = <AbstractMedia>[];

    listOfMedias.add(media1);
    listOfMedias.add(media2);
    listOfMedias.add(media3);

    when(mockMediasEvent.loadMedias(event))
        .thenAnswer((_) async => MediasShowed(listOfMedias));

    blocMedias.add(LoadMediaOfOneEvent(event));

    await expectLater(blocMedias.state, isA<MediasShowedError>());
  });

DataHelper类：

class DataHelper {
  DataHelper.initialize(String collectionPath) {
    this.setCollection(collectionPath);
  }

  late String collectionPath;
  late String className;
  late CollectionReference<Map<String, dynamic>> collection;

  final FirebaseFirestore firebaseFirestore = FirebaseFirestore.instance;
}

解决思路 #

• 修改DataHelper支持依赖注入
  当前DataHelper硬编码依赖FirebaseFirestore.instance，导致单元测试无法替换为Mock实例。修改构造函数，允许传入FirebaseFirestore实例：

  class DataHelper {
    final FirebaseFirestore firebaseFirestore;
  
    DataHelper.initialize(String collectionPath, {FirebaseFirestore? firestore}) 
      : firebaseFirestore = firestore ?? FirebaseFirestore.instance {
      this.setCollection(collectionPath);
    }
  
    // ... 其他原有代码
  }
  

  这样测试时可以传入Mock的Firestore实例，避免连接真实服务。

• 使用Firestore Mock库替代真实实例
  引入cloud_firestore_mocks包，它提供了无需原生通道的MockFirebaseFirestore实现。在测试中初始化Mock实例并注入到DataHelper，模拟Firestore操作：

  test('Test load medias', () async {
    // 初始化Mock Firestore
    final mockFirestore = MockFirebaseFirestore();
    
    // 创建Mock的DataHelper实例，注入mockFirestore
    final mockDataHelperMedias = DataHelper.initialize('medias', firestore: mockFirestore);
    final mockDataHelperUsers = DataHelper.initialize('users', firestore: mockFirestore);
  
    // 模拟getAll方法返回预期媒体列表
    when(mockDataHelperMedias.getAll()).thenAnswer((_) async => listOfMedias);
    // 模拟getEntity方法返回用户实例
    when(mockDataHelperUsers.getEntity(any)).thenAnswer((_) async => mockUser);
  
    // 注入Mock实例到bloc或DataHelperFactory
    // ...
  
    blocMedias.add(LoadMediaOfOneEvent(event));
    await expectLater(blocMedias.state, isA<MediasShowed>());
  });
  

• 修正测试中的Mock逻辑
  当前测试Mock的是mockMediasEvent.loadMedias(event)，但实际loadMedias方法内部调用的是_dataHelperMediasEvent.getAll()和_dataHelperUsers.getEntity()，这些依赖未被Mock，导致触发真实Firestore调用。需要确保_dataHelperMediasEvent和_dataHelperUsers都是Mock实例，并正确Stub它们的方法。

• 移除测试中真实Firebase初始化
  单元测试无需连接真实Firebase服务，直接删除await Firebase.initializeApp();，避免尝试建立原生通道连接。

内容的提问来源于stack exchange，提问作者Esca