Akka: Testing interactions with the IO managers

Question

I'd like to unit test an actor that binds its self to local port using the Tcp IO manager e.g

IO(Tcp) ! Bind(self, new InetSocketAddress("localhost", port))

What I'd ideally like to do is get a TestProbe in place of the IO manager. This will have the added benefit of a unit test not opening a TCP connection.

Is this possible, and if so, could someone please provide an example of how to do it?

Answer 1

There's probably a few ways to achieve this. I'll pass along a couple in hopes that one works for you. The thing to keep in mind that calling IO(Tcp) just produces an ActorRef. So all you need to do is find a way to mock/step in front of that call and then work with that actor ref. Here are a couple of code samples showing a couple of solutions (sort of DI like):

This first one sets up a method to return the tcp manager and then overrides it in the unit test.

class Actor1 extends Actor{
  import context._
  import Tcp._

  def receive = {
    case "connect" =>
      tcp ! Bind(self, new InetSocketAddress("localhost", 8080))
  }

  def tcp:ActorRef = IO(Tcp)
}

class Actor1Spec(_system:ActorSystem) extends TestKit(_system) with Specification{
  import Tcp._

  def this() = this(ActorSystem("test"))

  trait scoping extends Scope{
    val tcpProbe = TestProbe()
    val testRef = TestActorRef(new Actor1{
      override def tcp = tcpProbe.ref
    })
  }

  "A request to connect" should{
    "send a message to connect to the Tcp Manager" in new scoping{
      testRef ! "connect"
      tcpProbe.expectMsg(Bind(testRef, new InetSocketAddress("localhost", 8080)))
    }
  }
}

This second one is very similar but instead passes in the tcp manager into the constructor.

class Actor2(tcpManager:ActorRef) extends Actor{
  import context._
  import Tcp._

  def receive = {
    case "connect" =>
      tcpManager ! Bind(self, new InetSocketAddress("localhost", 8080))
  }

}

class Actor2Spec(_system:ActorSystem) extends TestKit(_system) with Specification{
  import Tcp._

  def this() = this(ActorSystem("test"))

  trait scoping extends Scope{
    val tcpProbe = TestProbe()
    val testRef = TestActorRef(new Actor2(tcpProbe.ref))
  }

  "A request to connect" should{
    "send a message to connect to the Tcp Manager" in new scoping{
      testRef ! "connect"
      tcpProbe.expectMsg(Bind(testRef, new InetSocketAddress("localhost", 8080)))
    }
  }
}

Either of these could work for you, but again, there is no real magic here as long as you understand that the call to IO(Tcp) is just returning an ActorRef