investigate how stack traces can be improved

[rkuhn]

Consider the following test case:

  private def flop = async { assert(false, "this is FALSE") } // <--- SomeTests.scala:14

  @Test def two = async {
    val x = await(op)
    val y = await(flop).toString
    val z = await(op)
    val w = x + z
    y + w
  }

Currently the stack trace reported looks like this:

java.lang.AssertionError: assertion failed: this is FALSE
    at scala.Predef$.assert(Predef.scala:165)
    at com.rolandkuhn.asynctest.SomeTests$$anonfun$com$rolandkuhn$asynctest$SomeTests$$flop$1.apply$mcV$sp(SomeTests.scala:14)
    at com.rolandkuhn.asynctest.SomeTests$$anonfun$com$rolandkuhn$asynctest$SomeTests$$flop$1.apply(SomeTests.scala:14)
    at com.rolandkuhn.asynctest.SomeTests$$anonfun$com$rolandkuhn$asynctest$SomeTests$$flop$1.apply(SomeTests.scala:14)
    at scala.concurrent.impl.Future$PromiseCompletingRunnable.liftedTree1$1(Future.scala:24)
    at scala.concurrent.impl.Future$PromiseCompletingRunnable.run(Future.scala:24)
    at scala.concurrent.impl.ExecutionContextImpl$AdaptedForkJoinTask.exec(ExecutionContextImpl.scala:121)
    at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)
    at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.pollAndExecAll(ForkJoinPool.java:1253)
    at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1346)
    at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
    at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)

It would be nicer if we could somehow wrap the exception at the line which contains await(flop), giving the user a better clue what went wrong.