Testing a message sent to a child

ParentActorTest.scala

class ParentActorTest extends TestKit(ActorSystem("TestSystem")) with FunSuiteLike {
  test("Should delegate the important work to the client") {
    val testProbeForChild = TestProbe()
    val underTest = TestActorRef(new ParentActor(_ => testProbeForChild.ref))

    underTest ! "Go do some work"

    testProbeForChild.expectMsg("Go and do something important!")
  }
}