How can I run tests in parallel but get neatly ordered test output?

Question

I'm using sbt and JUnit to run tests for a large Scala project. I'm forking multiple JVMs for tests, and defining how tests should be grouped in the JVMs using testGrouping in Test.

The tests are running in parallel, but their output is interleaved, making it hard to read through. I have set logBuffered in Test := true, but that doesn't seem to be doing anything.

Here's a snippet from my settings:

parallelExecution in Test := true,
testForkedParallel in Test := false,
concurrentRestrictions in Global := Seq(Tags.limit(Tags.ForkedTestGroup, 8)),

testGrouping in Test := (definedTests in Test, javaOptions in Test) map groupBySuite,
testGrouping in Test := {
  val original: Seq[Tests.Group] = (testGrouping in Test).value

  original.map { group =>
    val forkOptions = ForkOptions(
      bootJars = Nil,
      javaHome = javaHome.value,
      connectInput = connectInput.value,
      outputStrategy = outputStrategy.value,
      runJVMOptions = (javaOptions in Test).value,
      workingDirectory = Some(baseDirectory.value),
      envVars = envVars.value
    )

    group.copy(runPolicy = Tests.SubProcess(forkOptions))
  }
},
logBuffered in Test := true,

How can I keep my tests running in parallel, but have the output somehow be buffered and displayed in order so that it is readable? Is there perhaps some setting I need to feed to outputStrategy in the forked JVM options?

There is a similar question here, but I am looking to keep my tests running in parallel.

Answer 1

See http://www.scala-sbt.org/1.x/docs/Parallel-Execution.html

parallelExecution in Test controls whether tests are mapped to separate tasks. To restrict the number of concurrently executing tests in all projects, use:

concurrentRestrictions in Global += Tags.limit(Tags.Test, 1)