Can I use Akka's TestEventListener without it polluting my test ouput via STDOUT? - scala

Question

As part of my testing, I am using EventFilter and TestEventListener to listen to log messages. However, doing so causes there to be a massive flood in my command prompt... which makes it very hard to see my tests happening.
Sample Code:
it("should send a welcome message to the user", SystemFortressTest) {
val stub = new SubFortressBuildingPermitRefTraitImplStub
EventFilter.debug(message = "SystemFortressExchange: Received Message: SystemOutput(List(JITMP Booted))", occurrences = 1) intercept {
stub.buildASubFortress(SystemFortressBlueprintRef)
}
}
this code works, but it floods me with debug level data because the TestEventListener prints to STDOUT by default (as it subclasses the default logger which is just straight STDOUT only logging)
I can roll my own logging abstraction that sits on top of Akka's and filter messages from there before it ever hits Akka's stuff... so it wouldn't pollute my command prompt... but that's an awful lot of fuss if there is a similar solution already available.
Problem is, if I use the SL4J Logger, it doesn't work with EventFilter.

Answer 1

What I do is:
akka.loglevel = DEBUG
akka.loggers = ["akka.event.slf4j.Slf4jLogger", "akka.testkit.TestEventListener"]
.. and then in my tests:
system.eventStream.publish(Mute(EventFilter.info()))
system.eventStream.publish(Mute(EventFilter.debug()))
This way:
errors and warnings are reported twice (but those should be fixed anyway :) )
debug and info messages are only reported through slf4j
you can still use eventfilters to check for specific messages (perhaps after unmuting them first)
Note that generally I consider testing for log messages a code smell though - usually better to check for more 'observable' behaviour. Perhaps publish an event to the eventstream.

Answer 2

You can configure log levels or completely turn off the logger likewise with other loggers So when you configure TestEventListener you can specify the logging as below.
akka.loggers=["akka.testkit.TestEventListener"]
akka.loglevel = OFF
Hope this helps

Answer 3

A solution is to create a new listener class that extends the TestEventListener and overrides the print method to either do nothing, or log through your preferred logging solution instead of printing directly to stdout. You then can specify your custom event listener as a logger in your application.conf under the akka.loggers option. (see details at https://doc.akka.io/docs/akka/2.5/scala/testing.html)
So your event listener would be:
package mypackage
import akka.testkit.TestEventListener
class SilentTestEventListener extends TestEventListener {
override def print(event: Any): Unit = ()
}
And you would add the following to application.conf:
akka {
loggers = [mypackage.SilentTestEventListener]
}
If you would turn of logging by altering the log level, or filter noisy logs by using an event filter, then you also wouldn't be able to listen to those logs in your tests, because that is also done with event filters: the logger only executes the filters on the logs until it finds the first one that filters out the log message. If it finds another such filter before the filter used in the test, then your test will never get notified about the log entry.
Another nicer solution would be to implement an event listener that defines its own way of handling logs instead of inheriting and modifying the behavior of the StdOutLogger (since you would expect a subclass of the StdOutLogger to log to stdout...), but this would require more effort than the hacky solution above, since you would have to duplicate the functionality of the TestEventListener.

Answer 4

When using SL4J, here is how we can setup. You will have to turn off sl4j logging to use TestEventListner for testing DEBUG logs.
class MyClassSpec extends TestKit(MyClassSpec.system) {
"MyClass" should "test something" in {
val actor = MyClassSpec.system.actorOf(Props(new MyClass()))
EventFilter.debug(message = s"Testing something", occurrences = 1) intercept {
actor ! "test"
}
}
}
object MyClassSpec {
val testConfiguation = ConfigFactory.parseString("""
akka.loglevel = DEBUG
akka.loggers = ["akka.testkit.TestEventListener"]
akka.use-slf4j=off
""")
implicit val system: ActorSystem = {
ActorSystem("MyClassSystem", testConfiguation )
}
}