如何正确测试Java中的模拟Akka演员？

Question

I'm very new with Akka and I'm trying to write some unit tests in Java. Consider the following actor:

public class Worker extends UntypedActor {

  @Override
  public void onReceive(Object message) throws Exception {

    if (message instanceof Work) {
      Work work = (Work) message;
      Result result = new Helper().processWork(work);
      getSender().tell(result, getSelf());
    } else {
      unhandled(message);
    }
  }

}

What is the proper way to intercept the call new Helper().processWork(work) ? On a side note, is there any recommended way to achieve dependency injection within Akka actors with Java?

Thanks in advance.

Answer 1

Your code is already properly testable:

• you can test your business logic separately, since you can just instantiate your Helper outside of the actor
• once you are sure that the Helper does what it is supposed to do, just send some inputs to the actor and observe that the right replies come back

Now if you need to have a “mocked” Worker to test some other component, just don't use a Worker at all, use a TestProbe instead. Where you would normally get the ActorRef of the Worker, just inject probe.getRef() .

So, how to inject that?

I'll assume that your other component is an Actor (because otherwise you won't have trouble applying whatever injection technique you normally use). Then there are three basic choices:

1. pass it in as constructor argument
2. send it within a message
3. if the actor creates the ref as its child, pass in the Props , possibly in an alternative constructor

The third case is probably what you are looking at (I'm guessing based on the actor class' name):

public class MyParent extends UntypedActor {
  final Props workerProps;

  public MyParent() {
    workerProps = new Props(...);
  }
  public MyParent(Props p) {
    workerProps = p;
  }

  ...
  getContext().actorOf(workerProps, "worker");
}

And then you can inject a TestProbe like this:

final TestProbe probe = new TestProbe(system);
final Props workerMock = new Props(new UntypedActorFactory() {
  public UntypedActor create() {
    return new UntypedActor() {
      @Override
      public void onReceive(Object msg) {
        probe.getRef().tell(msg, getSender());
      }
    };
  }
});
final ActorRef parent = system.actorOf(new Props(new UntypedActorFactory() {
  public UntypedActor create() {
    return new MyParent(workerMock);
  }
}), "parent");