测试在 Isolate 上运行代码的 Dart class

Question

我有一个在 Isolate 上执行计算的 Dart class。这是我的代码：

class Mapper {
  SendPort _isolateSendPort;
  Isolate _isolate;

  Mapper() {
    _asyncInit();
  }

  void _asyncInit() async {
    final receivePort = ReceivePort();
    _isolate = await Isolate.spawn(
      _mappingFunction,
      receivePort.sendPort,
    );
    _isolateSendPort = await receivePort.first;
  }

  static void _mappingFunction(SendPort callerSendPort) {
    final newIsolateReceivePort = ReceivePort();
    callerSendPort.send(newIsolateReceivePort.sendPort);

    newIsolateReceivePort.listen((dynamic message) {
        final crossIsolatesMessage =
          message as CrossIsolatesMessage<Input>;

        // some computations...

        crossIsolatesMessage.sender.send(output);
    });
  }

  Future<Output> map(Input input) async {
    final port = ReceivePort();
    _isolateSendPort.send(CrossIsolatesMessage<Input>(
      sender: port.sendPort,
      message: input,
    ));
    return port.map((event) => event as Output).first;
  }

  void dispose() {
    _isolate?.kill(priority: Isolate.immediate);
    _isolate = null;
  }
}

class CrossIsolatesMessage<T> {
  final SendPort sender;
  final T message;

  CrossIsolatesMessage({
    @required this.sender,
    this.message,
  });
}

此代码在我运行 Flutter 应用程序时运行良好。但是 public 方法 Future<Output> map(Input input) 的单元测试抛出一个错误 NoSuchMethodError 这意味着 _isolateSendPort 是空的。

单元测试代码如下：

test('Mapper map', () {
  final sut = Mapper();
  final inputDummy = Input('123');
  final resultFuture = sut.map(inputDummy);
  final expectedResult = Output('321');
  expectLater(resultFuture, completion(expectedResult));
});

这是一个错误：

NoSuchMethodError: The method 'send' was called on null.
Receiver: null
Tried calling: send(Instance of 'CrossIsolatesMessage<Input>')
dart:core                                                  Object.noSuchMethod

为什么在测试中出现这个错误？为此 class 编写测试的正确方法是什么？

Answer 1

问题已解决。

创建 _isolate 和 _isolateSendPort 是一个异步操作。这就是 _isolateSendPort 在测试中为 null 的原因。从 Mapper 构造函数调用方法 _asyncInit() 是创建隔离的错误方法。

这是使用惰性隔离初始化的工作解决方案：

class Mapper {
  SendPort _isolateSendPort;
  Isolate _isolate;

  void _initIsolate() async {
    final receivePort = ReceivePort();
    _isolate = await Isolate.spawn(
      _mappingFunction,
      receivePort.sendPort,
    );
    _isolateSendPort = await receivePort.first;
  }

  ...

  Future<Output> map(Input input) async {
    final port = ReceivePort();
    if (_isolateSendPort == null) {
      await _initIsolate();
    }
    _isolateSendPort.send(CrossIsolatesMessage<Input>(
      sender: port.sendPort,
      message: input,
    ));
    return port.map((event) => event as Output).first;
  }

  ...
}

测试在 Isolate 上运行代码的 Dart class

Testing Dart class that runs code on Isolate

unit-testing

flutter

dart

dart-isolates