Adds system properties visible from test cases in both case that "fork" is ture or false.

build.sbt

import com.google.cloud.datastore.testing.LocalDatastoreHelper

commands += Command.command("datastoreRun") { state =>
  val helper = LocalDatastoreHelper.create(1.0)
  helper.start()
  atExit {
    helper.stop()
  }
  addSystemPropertiesTo(state)(Seq(
    "datastore.host" -> helper.getOptions.getHost
  ))
}

def addSystemPropertiesTo(state: State)(a: Seq[(String, String)]): State =
  Project.extract(state).append(Seq(
    javaOptions in GlobalScope ++= a.map(e => s"-D${e._1}=${e._2}"),
    testOptions in GlobalScope  += Tests.Setup { loader =>

      val setProperty = loader.loadClass("java.lang.System")
        .getDeclaredMethod("setProperty"
          , classOf[String]
          , classOf[String])

      a.foreach(e =>
        setProperty.invoke(null, e._1, e._2)
      )
    }
  ), state)

def atExit(f: => Unit): Unit =
  java.lang.Runtime.getRuntime.addShutdownHook(new Thread {
    override def run(): Unit = try f catch { case _: Throwable => }
  })