How to test Akka Actor has stopped, when using scheduler?

ButterflyActor.sc

import java.util.concurrent.TimeUnit

import akka.actor.typed.Behavior
import akka.actor.typed.scaladsl.{Behaviors, TimerScheduler}
import scala.concurrent.duration._

class ButterflyActor(
    timers: TimerScheduler[TriggerMessage],
) {

  def initialState() = {
    scheduleTrigger(10.seconds)
    Behaviors.receiveMessage[TriggerMessage] { _ =>
      Behaviors.stopped
    }
  }

  private def scheduleTrigger(delay: Long): Unit = {
    val delayDuration = FiniteDuration(delay, TimeUnit.MILLISECONDS)
    timers.startSingleTimer(TriggerMessage(), delayDuration)
  }
}

case class TriggerMessage()

object ButterflyActor {
  def apply = {
    Behaviors.setup { context =>
      Behaviors.withTimers { timers =>
        new ButterflyActor(timers).initialState()
      }
    }
  }
}

ButterflySpec.sc

import akka.actor.testkit.typed.scaladsl.{ManualTime, ScalaTestWithActorTestKit}

import org.scalatest.funspec.AnyFunSpecLike
import org.scalatest.matchers.should.Matchers
import org.scalamock.scalatest.MockFactory
import scala.concurrent.duration._

class DelayedMessagingActorSpec
    extends ScalaTestWithActorTestKit(ManualTime.config)
    with AnyFunSpecLike
    with Matchers
{
  val manualTime: ManualTime = ManualTime()
  
  it("stops after 10 seconds") {
      val actor = testKit.spawn(ButterflyActor())
      manualTime.timePasses(10.seconds)
      // TODO: How do we check it stopped?
    }
}

Answer: Use TestProbes

val actor = testKit.spawn(ButterflyActor())
val probe = testKit.createTestProbe()
manualTime.timePasses(10.seconds)
probe.expectTerminated(actor, 10.millis)