specs2 thread dump on test timeout

build.sbt

name := "specs2-thread-dump-on-timeout"

scalaVersion := "2.12.1"

val specs2Version = "3.8.6"

libraryDependencies ++= Seq(
  "org.specs2" %% "specs2-core" % specs2Version,
  "org.specs2" %% "specs2-matcher-extra" % specs2Version
)

WhyYouTimeoutSpec.scala

package com.bfritz
package specs2

import scala.collection.JavaConverters._
import org.specs2.concurrent.ExecutionEnv
import org.specs2.control.Debug._
import org.specs2.execute.AsResult
import org.specs2.matcher._
import org.specs2.mutable.{Around, Specification}
import org.specs2.specification.Scope

import scala.concurrent.duration._

class WhyYouTimeoutSpec extends Specification {

  "interrupt blocking sleep()" >> new MonitoredContext {
    Thread.sleep(5000)
    ok
  }

  trait MonitoredContext extends Scope with ThreadDumpOnTimeout
}

trait ThreadDumpOnTimeout extends Around with TerminationMatchers {
  implicit val executionEnv = ExecutionEnv.fromGlobalExecutionContext

  def dumpOnTimeout(s: String, timeout: Duration): String = {

    def expandFrames(frames: Array[StackTraceElement]) = frames.map(f => s"  $f\n").mkString

    val dumpedThreads = for {
      e <- Thread.getAllStackTraces().asScala
    } yield s"${e._1}\n${expandFrames(e._2)}"

    s"Timeout after $timeout with thread dump:\n\n${dumpedThreads.mkString("\n\n")}".pp
    s"Timeout after $timeout"
  }

  override def around[T: AsResult](t: => T) = {
    val timeout: Duration = 100.millis
    // "before".pp
    lazy val result = t
    val termination = terminate(retries = 1, sleep = timeout).orSkip(dumpOnTimeout(_, timeout))(createExpectable(t))
    // "after".pp
    if (!termination.toResult.isSkipped) AsResult(result)
    else termination.toResult
  }
}

And a hacky way to error on timeout:

override def around[T: AsResult](t: => T) = {
    ...
    if (!termination.toResult.isSkipped) AsResult(result)
    else Error(termination.message, new NoTrace)
  }

  class NoTrace extends RuntimeException {
    override def fillInStackTrace(): Throwable = null
  }
}