Scala akka actor system - RuntimeException when loading extension - scala

Question

I am new with scala and I face the following problem.
import akka.actor.Actor
import akka.actor.Props
import akka.event.Logging
import akka.actor.ActorSystem
object test extends App {
val system = ActorSystem("hello-world")
val myActor = system.actorOf(Props[MyActor], "myactor2")
}
class MyActor extends Actor {
val log = Logging(context.system, this)
val props1 = Props[MyActor]
def receive = {
case "test" => log.info("received test")
case _ => log.info("received unknown message")
}
val child = context.actorOf(Props[MyActor], name = "myChild")
}
So when I run it, I receive
[error] (run-main-1) java.lang.RuntimeException: While trying to load extension [akka.actor.InstanceCountingExtension]
java.lang.RuntimeException: While trying to load extension [akka.actor.InstanceCountingExtension]
at akka.actor.ActorSystemImpl.$anonfun$loadExtensions$1(ActorSystem.scala:906)
at scala.collection.Iterator.foreach(Iterator.scala:929)
at scala.collection.Iterator.foreach$(Iterator.scala:929)
at scala.collection.AbstractIterator.foreach(Iterator.scala:1406)
at scala.collection.IterableLike.foreach(IterableLike.scala:71)
...
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
Caused by: java.lang.ClassNotFoundException: akka.actor.InstanceCountingExtension
at java.lang.ClassLoader.findClass(ClassLoader.java:530)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
[trace] Stack trace suppressed: run last compile:run for the full output.
java.lang.RuntimeException: Nonzero exit code: 1
at scala.sys.package$.error(package.scala:27)
The problem is the ActorSystem, but i can't understand why. When I delete the system an myActor everything works fine. It even works when i make it only val system = ActorSystem but then system couldn't create actorOf.

Answer 1

You probably have this setting in your application.conf
akka.library-extensions += "akka.actor.InstanceCountingExtension"
This is an actor system extension used by akka-actor-tests to make assertions about the number of actor instances currently running in a system.
I don't think this is intended as an extension to be used by applications, it is more like a test utility.
However, depending on what you need:
if you just want to run your program, just delete the configuration line above, and all should be fine
if you need the extension for some reason, import akka-actor-tests test jar, or alternatively make sure you got this class available at runtime.

Answer 2

The problem was with the test folder. When I removed the test it started working.