Akka.NET–Testing the exceptional flow

We are currently building an actor based system using Akka.NET. Creating the system itself is a breeze thanks to Akka.NET, but the introduction of the actor model and actors makes testing somewhat harder.

The scenario we struggled the most with is when an Actor executes a task but reports no message back. In that case we don’t know what happened inside the actor itself making it hard to assert what is going on. Anyway today I wanted to talk about another scenario; how to test if an Actor throws an Exception.

I couldn’t find a good example that showed how to handle this test case, so here is how we do it(any feedback is welcome):

Remark: We are using NUnit in combination with Akka.TestKit.NUnit.

	public class SampleActor:ReceiveActor
	{
	public class Message{}
	public SampleActor()
	{
	Receive<SampleActor.Message>(message => DoSomething(message));
	}
	private void DoSomething(SampleActor.Message message)
	{
	throw new Exception();
	}
	}

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	[TestFixture]
	public class SampleActorTests : TestKit
	{
	[Test]
	public void SampleActor_Should_Throw_An_Exception()
	{
	//Arrange
	var actor = Sys.ActorOf(Props.Create(() => new SampleActor()));
	var filter = CreateEventFilter(Sys);
	//Act & Assert
	filter.Exception<Exception>().Expect(1,TimeSpan.FromSeconds(3), () => { actor.Tell(new SampleActor.Message()); });
	}
	}

view raw SampleActorTests.cs hosted with ❤ by GitHub