Akka.net and Unit tests

Question

I would like to use Akka.net TestKit for writing Unit tests, but I have a question. I have a class SubscriptionService which is responsible for transmitting messages to the selected actors.

public class SubscriptionService : ReceiveActor
{
    private readonly ActorSelection service1;

    private readonly ActorSelection service2;

    public SubscriptionService()
    {
        this.service1 = Context.ActorSelection("Service1");
        this.service2 = Context.ActorSelection("Service2");

        this.Receive<RequestMessage>(message => this.ProcessRequestMessage(message));
    }

    private void ProcessRequestMessage(RequestMessage message)
    {
        this.service1.Tell(message);
        this.service2.Tell(message);
    }

How can I test this behavior? I created this test but in this test I get the exception. "Additional information: Assert.Fail failed. Failed: Timeout 00:00:03 while waiting for a message"

[TestClass]
public class SubscriptionServiceUnitTests : TestKit
{
    [TestMethod]
    public void Test1()
    {
        var subscriptionServiceRef = this.ActorOfAsTestActorRef<SubscriptionService>("SubscriptionService");

        subscriptionServiceRef.Tell(new RequestMessage());

        var answer = this.ExpectMsg<RequestMessage>();
    }

I mean How can I get message for service1 and service2 in Test1 method ?

Answer 1

ExpectMsg works only when combined with special kind of an actor called TestActor. You can access/create it from test kit. It's role is to catch and verify messages send to it.

If you redesign your SubscriptionService actor a little, you could pass test actor refs to it. The easiest way to do so is to simply inject actor refs through actor constructor - I've used ICanTell interface, which is the more general form, implemented by both actor refs and actor selection:

public class SubscriptionService : ReceiveActor
{
    private readonly ICanTell service1;
    private readonly ICanTell service2;

    public SubscriptionService(ICanTell service1, ICanTell service2)
    {
        this.service1 = service1;
        this.service2 = service2;
        this.Receive<RequestMessage>(message => this.ProcessRequestMessage(message));
    }

This way you may create your actor using:

Context.ActorOf(Props.Create(() => new SubscriptionService(Context.ActorSelection("Service1"), Context.ActorSelection("Service2")));

To test it, in your TestKit spec class initialize it using either TestActor or TestProbe.