Mocking logger in Play! 2 Framework

Question

I have a Play! 2 application (Scala) and there I have some classes that need to perform logging when they get errors.

I would like to be able to unit test that these logging actions actually take place in the right conditions. To do so, I need to be able to mock the logger, but I am getting some issues with Mockito. What I have (simplified) looks like

import play.api.{ Logger, LoggerLike }

trait BaseService {
  val log: LoggerLike

  def fail(reason: String) {
    log.error(reason)
   }
}

object Service extends BaseService {
  val log = Logger
}

and then in the tests

import org.specs2.mutable._
import org.specs2.mock._
import services.BaseService

object Service extends BaseService with Mockito {
  val log = mock[play.api.Logger]

  def verify(key: String) = {
    there was one(log).error(key)
  }
}

class ServiceSpec extends Specification {
  "failures should be logged" in {
    Service.fail("foo")
    Service.verify("foo")
  }
}

But I get the error

[error]     NullPointerException: null (Logger.scala:43)
[error] play.api.LoggerLike$class.isErrorEnabled(Logger.scala:43)
[error] play.api.Logger.isErrorEnabled(Logger.scala:147)
[error] play.api.LoggerLike$class.error(Logger.scala:127)
[error] play.api.Logger.error(Logger.scala:147)
[error] services.BaseService$class.fail(Service.scala:19)
[error] Service$.fail(ServiceSpec.scala:11)
...

I tried adding

log.isErrorEnabled returns true
log.error(any[String]) returns {}

but then even the initialization of Service fails.

score 1 · Accepted Answer · edited May 23 '17 at 11:56

I'm not much of a Mockito expert, but I think your mock is malfunctioning here since the stack trace shows the actual play Logger methods being called. This is likely because you're trying to mock a Scala object here. If instead you mock the trait like

 val log = mock[play.api.LoggerLike]

you'll get past this specific error and on to the next problem - your verification doesn't work:

[error]   The mock was not called as expected: 
[error] Argument(s) are different! Wanted:
[error] loggerLike.error(
[error]     ($anonfun$apply$mcV$sp$1) <function0>
[error] );
[error] -> at Service$$anonfun$verify$1.apply$mcV$sp(ServiceSpec.scala:10)
[error] Actual invocation has different arguments:
[error] loggerLike.error(
[error]     ($anonfun$fail$1) <function0>
[error] );
[error] -> at services.BaseService$class.fail(x.scala:57)
[error]  (ServiceSpec.scala:17)

This is caused by the fact that log messages are passed as by-name arguments (and thus anonymous functions) instead of strings, see this question for further discussion.

Thank you, this was exactly the issue! Now it remains to be cleared how to work around pass-by-name. The solution in the question you posted looks a bit ugly, but hopefully I will be able to massage it into something more clear. — Andrea, Aug 31 '12 at 09:10

Mocking logger in Play! 2 Framework

1 Answers1