add dispatcher.shutdown() at app stop and make core pool size smaller to let the tests run

akka-actor/src/main/scala/akka/AkkaApplication.scala

@@ -214,4 +214,6 @@ class AkkaApplication(val name: String, val config: Configuration) extends Actor
     guardian.stop()
   }
 
+  terminationFuture.onComplete(_ ⇒ dispatcher.shutdown())
+
 }

config/akka.test.conf

@@ -9,7 +9,7 @@ akka {
   event-handler-level = "WARNING"
   actor {
     default-dispatcher {
-      core-pool-size = 8
+      core-pool-size = 4
       max-pool-size  = 32
     }
   }