Akka testing: it's a good idea to tell your actor system to leave a dead top-level actor dead. See: http://blog.jessitron.com/2014/03/testing-in-akka-sneaky-automatic.html

stayingDead.scala

// In real life, it's great that stuff gets restarted when it fails.
// In testing, we'd rather know that it failed.

import akka.actor._
class DyingActor extends Actor {
  def receive = { case "die" => throw new Exception("poo") }
}

// Default config, everything restarts automatically
val system = ActorSystem("ordinary")
val dyingActor = val system.actorOf(Props(new DyingActor))
dyingActor.isTerminated
// false
dyingActor ! "die"
dyingActor.isTerminated
// false -- no indication that the actor was restarted

// so let's configure one that won't restart it
import com.typesafe.config.ConfigFactory
val stoppingConfigStr = """ akka.actor.guardian-supervisor-strategy = "akka.actor.StoppingSupervisorStrategy" """
val stoppingConfig = ConfigFactory.parseString(stoppingConfigStr)

val tenderSystem = ActorSystem("sensitive", stoppingConfig)
val stayingDeadActor = tenderSystem.actorOf(Props(new DyingActor))
stayingDeadActor.isTerminated
// false
stayingDeadActor ! "die"
stayingDeadActor.isTerminated
// true -- this is something we can check in our tests

Great tip!

I'd recommend to avoid actorRef.isTerminated—it is not reliable (in the sense that the only guarantee is that when it returns true it will always return true after that)
The best solution is to use DeathWatch + TestKit's expectTerminated!