runAll.sbt

val runAll = taskKey[Unit]("run all main") 

runAllIn(Compile)

def runAllIn(config: Configuration) = {
  runAll in config := {
    val r = (runner in run).value
    val classpath = (fullClasspath in config).value
    val log = streams.value.log
    (discoveredMainClasses in config).value.foreach(c =>
      r.run(c, classpath.map(_.data), Nil, log)
    )
  }
}