William Carter William Carter - 3 months ago 22
Scala Question

How to respond to an Ask pattern with a failure using Akka TestKit?

I have an Akka Actor which uses the Ask pattern to retrieve a Future from a child actor and acts on both success and failure. I cannot work out how to mock out the child actor and respond with failures.

Here's the code:

import java.util.concurrent.TimeUnit
import akka.actor.{Actor, ActorRef, ActorSystem, Props}
import akka.pattern.ask
import akka.testkit.{ImplicitSender, TestKitBase, TestProbe}
import akka.util.Timeout
import org.specs2.mutable.Specification
import org.specs2.specification.Scope
import scala.util.{Failure, Success}

class Parent(child: ActorRef) extends Actor {
implicit val timeout = Timeout(5, TimeUnit.SECONDS)
import context.dispatcher

override def receive: Receive = {
case "go" => {
val senderRef = sender()
(child ? "question").mapTo[String] onComplete {
case Success("answer") =>
senderRef ! "child responded with a successful answer"
case Failure(throwable) =>
senderRef ! "child responded with a failure"
}
}
}
}

class SimplifiedProblemSpec extends Specification {

"The Parent Actor" should {
"act on success" in new TestScope {
parent ! "go"
childProbe.expectMsg("question")
childProbe.reply("answer")
expectMsg("child responded with a successful answer")
}
"act on failure" in new TestScope {
parent ! "go"
childProbe.expectMsg("question")
// How to reply with failure?
expectMsg("child responded with a failure")
}
}

}

abstract class TestScope extends Scope with TestKitBase with ImplicitSender {
implicit lazy val system: ActorSystem = ActorSystem()

val childProbe = TestProbe()
val parent = system.actorOf(Props(classOf[Parent], childProbe.ref), "Parent")

}


Any help would be much appreciated.

Thank you

Answer

You can use Status.Failure case class from akka.actor package. From docs:

This class/message type is preferably used to indicate failure of some operation performed. As an example, it is used to signal failure with AskSupport is used (ask/?).