Java : How should Futures be handled when Unit testing?

[Adam Daines]

Hi all,

I've got a question in relation to the unit testing of a piece of non actor code that produces a Future<ActorRef> via performing an actorSelection().resolveOne on the ActorSystem.

Within the Future.onFailure() a value is being set that I would like to test but the Future is making use of the ActorSystem.dispatcher() which is therefore causing asynchronicity issues when attempting to Assert that the value has been set as expected.

I am currently performing a Thread.sleep() within the Unit test to provide enough time for the value to have been set but this is far from ideal! 

What is the best way to go about testing this type of code without having to sleep and wait? Is it possible to override the dispatcher that the ActorSystem returns with the CallingThreadDispatcher?

Thanks.

[Viktor Klang]

Does this help?

http://christopher-batey.blogspot.se/2014/02/testing-scala-futures-with-scalatest-20.html

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[Akka Team]

On Thu, Apr 9, 2015 at 1:33 PM, Viktor Klang <viktor...@gmail.com> wrote:

Does this help?

http://christopher-batey.blogspot.se/2014/02/testing-scala-futures-with-scalatest-20.html

That is for scala though. We usually use scala.concurrent.Await which can be used like this

  assert(Await.result(myFuture, timeoutDuration) == xyz)

This will block the test and wait until the future becomes ready. If the future completes then the assertion will run. If the future fails, then Await.result() will throw the exception. If the future does not complete during the time defined in timeoutDuration, then it will throw A TimeoutException.

-Endre

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[Viktor Klang]

Ouch, nice catch, now we've covered both the question and the alternative (Scala) :)

[Adam Daines]

Thank you both for the quick and helpful responses! 

Our issue is now resolved :)

Thanks.

[Adam Daines]

Hi again, 

At first it had appeared that the issue was fully resolved but the test I had written began to fail again intermittently.  

It appears that taking the approach Endre suggested does not quite work as I had expected. It appears that the Await triggers and unblocks at the moment that the Future gets completed which is before the .onSuccess & .onFailure have actually run. 

In my use case the variable (which is a deferredResult) is actually set inside the .onFailure, therefore I cannot do an assertion on it until after the .onFailure has finished running.

Any further assistance would be much appreciated.

Thanks.

[Viktor Klang]

Hi Adam,

I generally recommend against using onComplete, onSuccess and onFailure for that reason,

instead use map/flatMap/andThen/recover/recoverWith/transform