Flutter testing - Repository

repository.dart

//Note: This code is just for demonstration purpose

class Repository {
  final RemoteDateSource remoteDateSource;
  Repository(this.remoteDateSource);

  Future<Student> fetch() async {
    late String result;
    try {
      result = await remoteDateSource.fetch();
    } catch (e) {
      throw Failure(e);
    }
    Student student = Student.fromString(result);
    return student;
  }
}

class RemoteDateSource {
  Future<String> fetch() async {
    final result = await httpClient.get("");
    return result;
  }
}

where does Failure() class come from?