move code to src/test

* so that it compiles and tests pass
* fix some additional snip references in getting started

akka-docs/src/test/scala/docs/testkit/PlainWordSpec.scala

@@ -0,0 +1,30 @@
+/**
+ * Copyright (C) 2009-2017 Lightbend Inc. <http://www.lightbend.com>
+ */
+package docs.testkit
+
+//#plain-spec
+import akka.actor.ActorSystem
+import akka.testkit.{ ImplicitSender, TestActors, TestKit }
+import org.scalatest.{ BeforeAndAfterAll, Matchers, WordSpecLike }
+
+//#implicit-sender
+class MySpec() extends TestKit(ActorSystem("MySpec")) with ImplicitSender
+  with WordSpecLike with Matchers with BeforeAndAfterAll {
+  //#implicit-sender
+
+  override def afterAll {
+    TestKit.shutdownActorSystem(system)
+  }
+
+  "An Echo actor" must {
+
+    "send back messages unchanged" in {
+      val echo = system.actorOf(TestActors.echoActorProps)
+      echo ! "hello world"
+      expectMsg("hello world")
+    }
+
+  }
+}
+//#plain-spec