Synchronous behavior testing

You are viewing the documentation for the new actor APIs, to view the Akka Classic documentation, see Classic Testing.

The BehaviorTestKit provides a very nice way of unit testing a Behavior in a deterministic way, but it has some limitations to be aware of.

Certain BehaviorBehaviors will be hard to test synchronously and the BehaviorTestKit doesn’t support testing of all features. In those cases the asynchronous ActorTestKit is recommended. Example of limitations:

Spawning of FutureCompletionStage or other asynchronous task and you rely on a callback to complete before observing the effect you want to test.
Usage of scheduler is not supported.
EventSourcedBehavior can’t be fully tested, but it is possible to test the core functionality
Interactions with other actors must be stubbed.
Blackbox testing style.
Supervision is not supported.

The BehaviorTestKit will be improved and some of these problems will be removed but it will always have limitations.

The following demonstrates how to test:

Spawning child actors
Spawning child actors anonymously
Sending a message either as a reply or to another actor
Sending a message to a child actor
Asking via the ActorContext

The examples below require the following imports:

Scala

sourceimport akka.actor.testkit.typed.CapturedLogEvent
import akka.actor.testkit.typed.Effect._
import akka.actor.testkit.typed.scaladsl.BehaviorTestKit
import akka.actor.testkit.typed.scaladsl.TestInbox
import akka.actor.typed._
import akka.actor.typed.scaladsl._
import com.typesafe.config.ConfigFactory
import org.slf4j.event.Level

Java

sourceimport akka.actor.testkit.typed.CapturedLogEvent;
import akka.actor.testkit.typed.Effect;
import akka.actor.testkit.typed.javadsl.BehaviorTestKit;
import akka.actor.testkit.typed.javadsl.TestInbox;
import akka.actor.typed.*;
import akka.actor.typed.javadsl.*;
import java.util.HashMap;
import java.util.List;
import java.util.Optional;
import java.time.Duration;

import com.typesafe.config.Config;
import org.slf4j.event.Level;

Each of the tests are testing an actor that based on the message executes a different effect to be tested:

Scala

sourceobject Hello {
  sealed trait Command
  case object CreateAnonymousChild extends Command
  case class CreateChild(childName: String) extends Command
  case class SayHelloToChild(childName: String) extends Command
  case object SayHelloToAnonymousChild extends Command
  case class SayHello(who: ActorRef[String]) extends Command
  case class LogAndSayHello(who: ActorRef[String]) extends Command
  case class AskAQuestion(who: ActorRef[Question]) extends Command
  case class GotAnAnswer(answer: String, from: ActorRef[Question]) extends Command
  case class NoAnswerFrom(whom: ActorRef[Question]) extends Command

  def apply(): Behaviors.Receive[Command] = Behaviors.receivePartial {
    case (context, CreateChild(name)) =>
      context.spawn(childActor, name)
      Behaviors.same
    case (context, CreateAnonymousChild) =>
      context.spawnAnonymous(childActor)
      Behaviors.same
    case (context, SayHelloToChild(childName)) =>
      val child: ActorRef[String] = context.spawn(childActor, childName)
      child ! "hello"
      Behaviors.same
    case (context, SayHelloToAnonymousChild) =>
      val child: ActorRef[String] = context.spawnAnonymous(childActor)
      child ! "hello stranger"
      Behaviors.same
    case (_, SayHello(who)) =>
      who ! "hello"
      Behaviors.same
    case (context, LogAndSayHello(who)) =>
      context.log.info("Saying hello to {}", who.path.name)
      who ! "hello"
      Behaviors.same
    case (context, AskAQuestion(who)) =>
      implicit val timeout: Timeout = 10.seconds
      context.ask[Question, Answer](who, Question("do you know who I am?", _)) {
        case Success(answer) => GotAnAnswer(answer.a, who)
        case Failure(_)      => NoAnswerFrom(who)
      }
      Behaviors.same
    case (context, GotAnAnswer(answer, from)) =>
      context.log.info2("Got an answer [{}] from {}", answer, from)
      Behaviors.same
    case (context, NoAnswerFrom(from)) =>
      context.log.info("Did not get an answer from {}", from)
      Behaviors.same
  }

  // Included in Hello for brevity
  case class Question(q: String, replyTo: ActorRef[Answer])
  case class Answer(a: String)
}

Java

sourcepublic static class Hello extends AbstractBehavior<Hello.Command> {

  public interface Command {}

  public static class CreateAChild implements Command {
    public final String childName;

    public CreateAChild(String childName) {
      this.childName = childName;
    }
  }

  public enum CreateAnAnonymousChild implements Command {
    INSTANCE
  }

  public static class SayHelloToChild implements Command {
    public final String childName;

    public SayHelloToChild(String childName) {
      this.childName = childName;
    }
  }

  public enum SayHelloToAnonymousChild implements Command {
    INSTANCE
  }

  public static class SayHello implements Command {
    public final ActorRef<String> who;

    public SayHello(ActorRef<String> who) {
      this.who = who;
    }
  }

  public static class LogAndSayHello implements Command {
    public final ActorRef<String> who;

    public LogAndSayHello(ActorRef<String> who) {
      this.who = who;
    }
  }

  public static class AskAQuestion implements Command {
    public final ActorRef<Question> who;

    public AskAQuestion(ActorRef<Question> who) {
      this.who = who;
    }
  }

  public static class GotAnAnswer implements Command {
    public final String answer;
    public final ActorRef<Question> from;

    public GotAnAnswer(String answer, ActorRef<Question> from) {
      this.answer = answer;
      this.from = from;
    }
  }

  public static class NoAnswerFrom implements Command {
    public final ActorRef<Question> whom;

    public NoAnswerFrom(ActorRef<Question> whom) {
      this.whom = whom;
    }
  }

  public static class Question {
    public final String q;
    public final ActorRef<Answer> replyTo;

    public Question(String q, ActorRef<Answer> replyTo) {
      this.q = q;
      this.replyTo = replyTo;
    }
  }

  public static class Answer {
    public final String a;

    public Answer(String a) {
      this.a = a;
    }
  }

  public static Behavior<Command> create() {
    return Behaviors.setup(Hello::new);
  }

  private Hello(ActorContext<Command> context) {
    super(context);
  }

  @Override
  public Receive<Command> createReceive() {
    return newReceiveBuilder()
        .onMessage(CreateAChild.class, this::onCreateAChild)
        .onMessage(CreateAnAnonymousChild.class, this::onCreateAnonymousChild)
        .onMessage(SayHelloToChild.class, this::onSayHelloToChild)
        .onMessage(SayHelloToAnonymousChild.class, this::onSayHelloToAnonymousChild)
        .onMessage(SayHello.class, this::onSayHello)
        .onMessage(LogAndSayHello.class, this::onLogAndSayHello)
        .onMessage(AskAQuestion.class, this::onAskAQuestion)
        .onMessage(GotAnAnswer.class, this::onGotAnAnswer)
        .onMessage(NoAnswerFrom.class, this::onNoAnswerFrom)
        .build();
  }

  private Behavior<Command> onCreateAChild(CreateAChild message) {
    getContext().spawn(Child.create(), message.childName);
    return Behaviors.same();
  }

  private Behavior<Command> onCreateAnonymousChild(CreateAnAnonymousChild message) {
    getContext().spawnAnonymous(Child.create());
    return Behaviors.same();
  }

  private Behavior<Command> onSayHelloToChild(SayHelloToChild message) {
    ActorRef<String> child = getContext().spawn(Child.create(), message.childName);
    child.tell("hello");
    return Behaviors.same();
  }

  private Behavior<Command> onSayHelloToAnonymousChild(SayHelloToAnonymousChild message) {
    ActorRef<String> child = getContext().spawnAnonymous(Child.create());
    child.tell("hello stranger");
    return Behaviors.same();
  }

  private Behavior<Command> onSayHello(SayHello message) {
    message.who.tell("hello");
    return Behaviors.same();
  }

  private Behavior<Command> onLogAndSayHello(LogAndSayHello message) {
    getContext().getLog().info("Saying hello to {}", message.who.path().name());
    message.who.tell("hello");
    return Behaviors.same();
  }

  private Behavior<Command> onAskAQuestion(AskAQuestion message) {
    getContext()
        .ask(
            Answer.class,
            message.who,
            Duration.ofSeconds(10),
            (ActorRef<Answer> ref) -> new Question("do you know who I am?", ref),
            (response, throwable) -> {
              if (response != null) {
                return new GotAnAnswer(response.a, message.who);
              } else {
                return new NoAnswerFrom(message.who);
              }
            });
    return Behaviors.same();
  }

  private Behavior<Command> onGotAnAnswer(GotAnAnswer message) {
    getContext().getLog().info("Got an answer[{}] from {}", message.answer, message.from);
    return Behaviors.same();
  }

  private Behavior<Command> onNoAnswerFrom(NoAnswerFrom message) {
    getContext().getLog().info("Did not get an answer from {}", message.whom);
    return Behaviors.same();
  }
}

For creating a child actor a noop actor is created:

Scala

sourceval childActor = Behaviors.receiveMessage[String] { _ =>
  Behaviors.same[String]
}

Java

sourcepublic static class Child {
  public static Behavior<String> create() {
    return Behaviors.receive((context, message) -> Behaviors.same());
  }
}

All of the tests make use of the BehaviorTestKitBehaviorTestKit to avoid the need for a real ActorContext. Some of the tests make use of the TestInboxTestInbox which allows the creation of an ActorRefActorRef that can be used for synchronous testing, similar to the TestProbe used for asynchronous testing.

Spawning children

With a name:

Scala

sourceval testKit = BehaviorTestKit(Hello())
testKit.run(Hello.CreateChild("child"))
testKit.expectEffect(Spawned(childActor, "child"))

Java

sourceBehaviorTestKit<Hello.Command> test = BehaviorTestKit.create(Hello.create());
test.run(new Hello.CreateAChild("child"));
assertEquals("child", test.expectEffectClass(Effect.Spawned.class).childName());

Anonymously:

Scala

sourceval testKit = BehaviorTestKit(Hello())
testKit.run(Hello.CreateAnonymousChild)
testKit.expectEffect(SpawnedAnonymous(childActor))

Java

sourceBehaviorTestKit<Hello.Command> test = BehaviorTestKit.create(Hello.create());
test.run(Hello.CreateAnAnonymousChild.INSTANCE);
test.expectEffectClass(Effect.SpawnedAnonymous.class);

Sending messages

For testing sending a message a TestInboxTestInbox is created that provides an ActorRefActorRef and methods to assert against the messages that have been sent to it.

Scala

sourceval testKit = BehaviorTestKit(Hello())
val inbox = TestInbox[String]()
testKit.run(Hello.SayHello(inbox.ref))
inbox.expectMessage("hello")

Java

sourceBehaviorTestKit<Hello.Command> test = BehaviorTestKit.create(Hello.create());
TestInbox<String> inbox = TestInbox.create();
test.run(new Hello.SayHello(inbox.getRef()));
inbox.expectMessage("hello");

Another use case is sending a message to a child actor you can do this by looking up the TestInboxTestInbox for a child actor from the BehaviorTestKitBehaviorTestKit:

Scala

sourceval testKit = BehaviorTestKit(Hello())
testKit.run(Hello.SayHelloToChild("child"))
val childInbox = testKit.childInbox[String]("child")
childInbox.expectMessage("hello")

Java

sourceBehaviorTestKit<Hello.Command> testKit = BehaviorTestKit.create(Hello.create());
testKit.run(new Hello.SayHelloToChild("child"));
TestInbox<String> childInbox = testKit.childInbox("child");
childInbox.expectMessage("hello");

For anonymous children the actor names are generated in a deterministic way:

Scala

sourceval testKit = BehaviorTestKit(Hello())
testKit.run(Hello.SayHelloToAnonymousChild)
val child = testKit.expectEffectType[SpawnedAnonymous[String]]

val childInbox = testKit.childInbox(child.ref)
childInbox.expectMessage("hello stranger")

Java

sourceBehaviorTestKit<Hello.Command> testKit = BehaviorTestKit.create(Hello.create());
testKit.run(Hello.SayHelloToAnonymousChild.INSTANCE);
// Anonymous actors are created as: $a $b etc
TestInbox<String> childInbox = testKit.childInbox("$a");
childInbox.expectMessage("hello stranger");

An ask via ActorContext can be tested with the assistance of the Effect.AskInitiatedEffect.AskInitiated Effect. The request message is sent to the target recipient and can be obtained from the AskInitiated. The interaction may be completed by calling respondWith or timeout on the AskInitiated, and the transformation of the response or timeout into the requestor’s protocol may also be tested using the adaptResponse or adaptTimeout methods.

Scala

sourceval testKit = BehaviorTestKit(Hello())
val askee = TestInbox[Hello.Question]()
testKit.run(Hello.AskAQuestion(askee.ref))

// The ask message is sent and can be inspected via the TestInbox
// note that the "replyTo" address is not directly predictable
val question = askee.receiveMessage()

// The particulars of the `context.ask` call are captured as an Effect
val effect = testKit.expectEffectType[AskInitiated[Hello.Question, Hello.Answer, Hello.Command]]

testKit.clearLog()

// The returned effect can be used to complete or time-out the ask at most once
effect.respondWith(Hello.Answer("I think I met you somewhere, sometime"))
// (since we completed the ask, timing out is commented out)
// effect.timeout()

// Completing/timing-out the ask is processed synchronously
testKit.logEntries().size shouldBe 1

// The message (including the synthesized "replyTo" address) can be inspected from the effect
val sentQuestion = effect.askMessage

// The response adaptation can be tested as many times as you want without completing the ask
val response1 = effect.adaptResponse(Hello.Answer("No.  Who are you?"))
val response2 = effect.adaptResponse(Hello.Answer("Hey Joe!"))

// ... as can the message sent on a timeout
val timeoutResponse = effect.adaptTimeout

// The response timeout can be inspected
val responseTimeout = effect.responseTimeout

Java

sourceBehaviorTestKit<Hello.Command> test = BehaviorTestKit.create(Hello.create());
TestInbox<Hello.Question> askee = TestInbox.create();
test.run(new Hello.AskAQuestion(askee.getRef()));

Hello.Question question = askee.receiveMessage();
// Note that the replyTo address in the message is not a priori predictable, so shouldn't be
// asserted against
assertEquals(question.q, "do you know who I am?");

// Retrieve a description of the performed ask
@SuppressWarnings("unchecked")
Effect.AskInitiated<Hello.Question, Hello.Answer, Hello.Command> effect =
    test.expectEffectClass(Effect.AskInitiated.class);

test.clearLog();

// The effect can be used to complete or time-out the ask at most once
effect.respondWith(new Hello.Answer("I think I met you somewhere, sometime"));
// commented out because we've completed the ask
// effect.timeout();

// Completing/timing-out the ask is processed synchronously
List<CapturedLogEvent> allLogEntries = test.getAllLogEntries();
assertEquals(allLogEntries.size(), 1);

// The message, including the synthesized "replyTo", can be inspected from the effect
assertEquals(question, effect.askMessage());

// The response adaptation can be tested as many times as you want without completing the ask
Hello.Command response1 = effect.adaptResponse(new Hello.Answer("No.  Who are you?"));
assertEquals(((Hello.GotAnAnswer) response1).answer, "No.  Who are you?");

// ... as can the message sent on a timeout
assertTrue(effect.adaptTimeout() instanceof Hello.NoAnswerFrom);

// The response timeout is captured
assertEquals(effect.responseTimeout().toSeconds(), 10L);

Testing other effects

The BehaviorTestKitBehaviorTestKit keeps track other effects you can verify, look at the sub-classes of EffectEffect

SpawnedAdapter
Stopped
Watched
WatchedWith
Unwatched
Scheduled
TimerScheduled
TimerCancelled

Checking for Log Messages

The BehaviorTestKitBehaviorTestKit also keeps track of everything that is being logged. Here, you can see an example on how to check if the behavior logged certain messages:

Scala

sourceval testKit = BehaviorTestKit(Hello())
val inbox = TestInbox[String]("Inboxer")
testKit.run(Hello.LogAndSayHello(inbox.ref))
testKit.logEntries() shouldBe Seq(CapturedLogEvent(Level.INFO, "Saying hello to Inboxer"))

Java

sourceBehaviorTestKit<Hello.Command> test = BehaviorTestKit.create(Hello.create());
TestInbox<String> inbox = TestInbox.create("Inboxer");
test.run(new Hello.LogAndSayHello(inbox.getRef()));

List<CapturedLogEvent> allLogEntries = test.getAllLogEntries();
assertEquals(1, allLogEntries.size());
CapturedLogEvent expectedLogEvent =
    new CapturedLogEvent(
        Level.INFO,
        "Saying hello to Inboxer",
        Optional.empty(),
        Optional.empty(),
        new HashMap<>());
assertEquals(expectedLogEvent, allLogEntries.get(0));

See the other public methods and API documentation on BehaviorTestKitBehaviorTestKit for other types of verification.