Identify exact failed match from failed Scalacheck property in specs2 - scala

Question

I am running a specs2 test suite from sbt, using the test command. When a ScalaCheck property fails, I just get to see the filename and line number in my code where the specs2 match fails - which is not very useful when that happens to be a utility method which does a common type of check that I am frequently doing. A stack trace would be better.
I've tried the last command in sbt, but that doesn't display the stack trace I'm looking for. The only stack trace last displays is this generic one:
java.lang.RuntimeException: Tests unsuccessful
at scala.sys.package$.error(package.scala:27)
at scala.Predef$.error(Predef.scala:66)
at sbt.Tests$.showResults(Tests.scala:168)
at sbt.Defaults$$anonfun$testTasks$5.apply(Defaults.scala:279)
at sbt.Defaults$$anonfun$testTasks$5.apply(Defaults.scala:279)
at sbt.Scoped$$anonfun$hf2$1.apply(Structure.scala:473)
at sbt.Scoped$$anonfun$hf2$1.apply(Structure.scala:473)
at scala.Function1$$anonfun$compose$1.apply(Function1.scala:41)
at sbt.Scoped$Reduced$$anonfun$combine$1$$anonfun$apply$11.apply(Structure.scala:295)
at sbt.Scoped$Reduced$$anonfun$combine$1$$anonfun$apply$11.apply(Structure.scala:295)
at sbt.$tilde$greater$$anonfun$$u2219$1.apply(TypeFunctions.scala:40)
at sbt.std.Transform$$anon$5.work(System.scala:67)
at sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:221)
at sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:221)
at sbt.ErrorHandling$.wideConvert(ErrorHandling.scala:18)
at sbt.Execute.work(Execute.scala:227)
at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:221)
at sbt.Execute$$anonfun$submit$1.apply(Execute.scala:221)
at sbt.CompletionService$$anon$1$$anon$2.call(CompletionService.scala:26)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)
I also have FINEST logging level enabled in the java.util.logging properties file.
For now I am working around this issue using the Eclipse debugger, but that's unnecessarily heavyweight in some cases.

Answer 1

You can display the stacktrace failures by passing the failtrace argument on the command line. This is documented in the Arguments part of the User Guide.
Also you have to know that this stacktrace is filtered to avoid showing specs2's own stack so if you want to see everything you need to add fullstacktrace which is a shortcut for a TraceFilter that filters nothing.

Answer 2

I decided to take a different approach to identifying the failed match - using aka, like this:
def occurExactlyOnceInBody = be_===(1) ^^ { (s: String) => body.tails.count(_.startsWith(s)) aka "No. of occurences of " + s + " in body" }
The downside is this does need to be applied manually, but the upside is it's easier to understand the failures.