Testing message forwarding in akka.testkit.TestKit

Question

I want to test the following scenario:

Assume I have a parent actor, which creates two child actors like this.

class A extends Actor {
  def getActorOf(props: Props) = {
    context.actorOf(props, props.clazz.getTypeName)
  }

  def receive: Receive = {
    case "ping" => {
      val bChild = getActorOf(Props[B])
      val cChild = getActorOf(Props[C])
      Seq(bChild, cChild)
        .foreach(child => child ! "ping forwarded")
    }
  }
}

I want to test that if in case the parent get 'ping' he will send 'ping forwarded' message to both own children.

Is it possible to do this with TestKit?

Answer 1

Something like this, perhaps?

 class TestMe extends A {
   val (probeB, probeC) = (TestProbe(), TestProbe())
   override def getActorOf(props: Props) = props match {
     case Props(_, classOf[B], _) => probeB.ref
     case Props(_, classOf[C], _) => probeC.ref
   }
 }

 val fixture = TestActorRef[TestMe](Props[TestMe])
 fixture ! "ping" 
 fixture.underlyingActor.probeB.expectMsg("ping forwarded")
 fixture.underlyingActor.probeB.expectMsg("ping forwarded")

Personally, I prefer a more "traditional" approach, whenever possible:

 trait Forwarder {
   def startAndForward[T : ClassTag](message: Any)(implicit context: ActorContext) = {
     val actor = context.actorOf(Props[T])
     actor ! message
     actor
  }
}
object Forwarder extends Forwarder

 class A(f: Forwarder = Forwarder) extends Actor {

   def receive: Receive = {
     case m@"ping" => 
       f.startAndForward[B]("ping forwarded")     
       f.startAndForward[C]("ping forwarded")
       sender ! "pong"
   }
 }

Now, you can run your test in straightforward way:

 val fwd = mock[Forwarder]
 val fixture = context.actorOf(Props(new A(fwd)))
 fixture.ask("ping").futureValue shouldBe "pong"
 verify(fwd).startAndForward[B](ArgumentMatchers.eq("ping forwarded"))(any, any)
 verify(fwd).startAndForward[C](ArgumentMatchers.eq("ping forwarded"))(any, any)