Avoid TestConductorTransport unless needed, see #2586

* Due to the shutdown issues the TestConductorTransport is by
  default not active, but it's easy to activate it and exception
  will be thrown if trying to use the featues that require it, i.e
  blackhole, passThrow and throttle
* Documented

akka-cluster/src/multi-jvm/scala/akka/cluster/SplitBrainSpec.scala

@@ -27,6 +27,8 @@ case class SplitBrainMultiNodeConfig(failureDetectorPuppet: Boolean) extends Mul
           failure-detector.threshold = 4
         }""")).
     withFallback(MultiNodeClusterSpec.clusterConfig(failureDetectorPuppet)))
+
+  testTransport(on = true)
 }
 
 class SplitBrainWithFailureDetectorPuppetMultiJvmNode1 extends SplitBrainSpec(failureDetectorPuppet = true)

akka-cluster/src/multi-jvm/scala/akka/cluster/UnreachableNodeRejoinsClusterSpec.scala

@@ -21,6 +21,8 @@ case class UnreachableNodeRejoinsClusterMultiNodeConfig(failureDetectorPuppet: B
   val fourth = role("fourth")
 
   commonConfig(debugConfig(on = false).withFallback(MultiNodeClusterSpec.clusterConfig))
+
+  testTransport(on = true)
 }
 
 class UnreachableNodeRejoinsClusterWithFailureDetectorPuppetMultiJvmNode1 extends UnreachableNodeRejoinsClusterSpec(failureDetectorPuppet = true)

akka-docs/rst/dev/multi-node-testing.rst

@@ -207,6 +207,9 @@ surprising ways.
 
   * Don't issue a shutdown of the first node. The first node is the controller and if it shuts down your test will break.
 
+  * To be able to use ``blackhole``, ``passThrough``, and ``throttle`` you must activate the ``TestConductorTranport`` 
+    by specifying ``testTransport(on = true)`` in your MultiNodeConfig.
+
   * Throttling, shutdown and other failure injections can only be done from the first node, which again is the controller.
 
   * Don't ask for the address of a node using ``node(address)`` after the node has been shut down. Grab the address before

akka-remote-tests/src/main/scala/akka/remote/testconductor/Conductor.scala

@@ -24,6 +24,7 @@ import akka.util.{ Timeout }
 import scala.concurrent.util.{ Deadline, Duration }
 import scala.reflect.classTag
 import scala.concurrent.util.FiniteDuration
+import akka.ConfigurationException
 
 sealed trait Direction {
   def includes(other: Direction): Boolean
@@ -102,6 +103,9 @@ trait Conductor { this: TestConductorExt ⇒
   }
 
   /**
+   * To use this feature you must activate the TestConductorTranport by
+   * specifying `testTransport(on = true)` in your MultiNodeConfig.
+   *
    * Make the remoting pipeline on the node throttle data sent to or received
    * from the given remote peer. Throttling works by delaying packet submission
    * within the netty pipeline until the packet would have been completely sent
@@ -121,10 +125,14 @@ trait Conductor { this: TestConductorExt ⇒
    */
   def throttle(node: RoleName, target: RoleName, direction: Direction, rateMBit: Double): Future[Done] = {
     import Settings.QueryTimeout
+    requireTestConductorTranport()
     controller ? Throttle(node, target, direction, rateMBit.toFloat) mapTo classTag[Done]
   }
 
   /**
+   * To use this feature you must activate the TestConductorTranport by
+   * specifying `testTransport(on = true)` in your MultiNodeConfig.
+   *
    * Switch the Netty pipeline of the remote support into blackhole mode for
    * sending and/or receiving: it will just drop all messages right before
    * submitting them to the Socket or right after receiving them from the
@@ -136,10 +144,19 @@ trait Conductor { this: TestConductorExt ⇒
    */
   def blackhole(node: RoleName, target: RoleName, direction: Direction): Future[Done] = {
     import Settings.QueryTimeout
+    requireTestConductorTranport()
     controller ? Throttle(node, target, direction, 0f) mapTo classTag[Done]
   }
 
+  private def requireTestConductorTranport(): Unit =
+    if (!transport.isInstanceOf[TestConductorTransport])
+      throw new ConfigurationException("To use this feature you must activate the TestConductorTranport by " +
+        "specifying `testTransport(on = true)` in your MultiNodeConfig.")
+
   /**
+   * To use this feature you must activate the TestConductorTranport by
+   * specifying `testTransport(on = true)` in your MultiNodeConfig.
+   *
    * Switch the Netty pipeline of the remote support into pass through mode for
    * sending and/or receiving.
    *
@@ -149,6 +166,7 @@ trait Conductor { this: TestConductorExt ⇒
    */
   def passThrough(node: RoleName, target: RoleName, direction: Direction): Future[Done] = {
     import Settings.QueryTimeout
+    requireTestConductorTranport()
     controller ? Throttle(node, target, direction, -1f) mapTo classTag[Done]
   }
 

akka-remote-tests/src/main/scala/akka/remote/testkit/MultiNodeSpec.scala

@@ -19,6 +19,7 @@ import scala.concurrent.util.Duration
 import scala.concurrent.util.duration._
 import java.util.concurrent.TimeoutException
 import akka.remote.testconductor.RoleName
+import akka.remote.testconductor.TestConductorTransport
 import akka.actor.RootActorPath
 import akka.event.{ Logging, LoggingAdapter }
 
@@ -32,6 +33,7 @@ abstract class MultiNodeConfig {
   private var _roles = Vector[RoleName]()
   private var _deployments = Map[RoleName, Seq[String]]()
   private var _allDeploy = Vector[String]()
+  private var _testTransport = false
 
   /**
    * Register a common base config for all test participants, if so desired.
@@ -81,13 +83,24 @@ abstract class MultiNodeConfig {
 
   def deployOnAll(deployment: String): Unit = _allDeploy :+= deployment
 
+  /**
+   * To be able to use `blackhole`, `passThrough`, and `throttle` you must
+   * activate the TestConductorTranport by specifying
+   * `testTransport(on = true)` in your MultiNodeConfig.
+   */
+  def testTransport(on: Boolean): Unit = _testTransport = on
+
   private[testkit] lazy val myself: RoleName = {
     require(_roles.size > MultiNodeSpec.selfIndex, "not enough roles declared for this test")
     _roles(MultiNodeSpec.selfIndex)
   }
 
   private[testkit] def config: Config = {
-    val configs = (_nodeConf get myself).toList ::: _commonConf.toList ::: MultiNodeSpec.nodeConfig :: MultiNodeSpec.baseConfig :: Nil
+    val transportConfig =
+      if (_testTransport) ConfigFactory.parseString("akka.remote.transport=" + classOf[TestConductorTransport].getName)
+      else ConfigFactory.empty
+
+    val configs = (_nodeConf get myself).toList ::: _commonConf.toList ::: transportConfig :: MultiNodeSpec.nodeConfig :: MultiNodeSpec.baseConfig :: Nil
     configs reduce (_ withFallback _)
   }
 
@@ -175,7 +188,6 @@ object MultiNodeSpec {
 
   private[testkit] val nodeConfig = mapToConfig(Map(
     "akka.actor.provider" -> "akka.remote.RemoteActorRefProvider",
-    "akka.remote.transport" -> "akka.remote.testconductor.TestConductorTransport",
     "akka.remote.netty.hostname" -> selfName,
     "akka.remote.netty.port" -> selfPort))
 

akka-remote-tests/src/multi-jvm/scala/akka/remote/testconductor/TestConductorSpec.scala

@@ -23,6 +23,8 @@ object TestConductorMultiJvmSpec extends MultiNodeConfig {
 
   val master = role("master")
   val slave = role("slave")
+
+  testTransport(on = true)
 }
 
 class TestConductorMultiJvmNode1 extends TestConductorSpec