我有一个演员的形式：

class TestActor(repo: Repo) extends Actor {
  implicit val executionContext: ExecutionContext = context.dispatcher

  def receive: Receive = {
    ...
  }

  def testMethod(stringSeq: Seq[String]): String =
       ...
    }
}

我只想测试方法testMethod。
我尝试将测试用例编写为：

class TestActorSpec
    extends TestKit(ActorSystem("TestActorSpec"))
    with WordSpecLike
    with Matchers
    with JsonSupport
    with MockitoSugar
    with BeforeAndAfterAll
    with ImplicitSender {
  override def afterAll: Unit = TestKit.shutdownActorSystem(system)

  implicit val futureDuration: FiniteDuration = 60.seconds
  implicit val timeout: Timeout               = 10.seconds
  val mockedRepo               = mock[Repo]

  val testActorRef: ActorRef = system.actorOf(
    TestActor.props(mockedRepo)
  )

  "TestActorSpec" should {
    "be able to get data " in {

    }
  }
}

如何从testActorRef访问方法testMethod？
我也试探着：

TestActorRef[TestActor].underlyingActor.testMethod(Seq("data"))

这对我不起作用。