clarify docs of ActorTestKit.stop, #24165

akka-actor-testkit-typed/src/main/scala/akka/actor/testkit/typed/javadsl/ActorTestKit.scala

@@ -153,10 +153,14 @@ final class ActorTestKit private[akka] (delegate: akka.actor.testkit.typed.scala
   def spawn[T](behavior: Behavior[T], name: String, props: Props): ActorRef[T] = delegate.spawn(behavior, name, props)
   /**
    * Stop the actor under test and wait until it terminates.
+   * It can only be used for actors that were spawned by this `ActorTestKit`.
+   * Other actors will not be stopped by this method.
    */
   def stop[T](ref: ActorRef[T]): Unit = delegate.stop(ref)
   /**
    * Stop the actor under test and wait `max` until it terminates.
+   * It can only be used for actors that were spawned by this `ActorTestKit`.
+   * Other actors will not be stopped by this method.
    */
   def stop[T](ref: ActorRef[T], max: Duration): Unit = delegate.stop(ref, max.asScala)
 

akka-actor-testkit-typed/src/main/scala/akka/actor/testkit/typed/scaladsl/ActorTestKit.scala

@@ -177,6 +177,8 @@ final class ActorTestKit private[akka] (val name: String, val config: Config, se
 
   /**
    * Stop the actor under test and wait until it terminates.
+   * It can only be used for actors that were spawned by this `ActorTestKit`.
+   * Other actors will not be stopped by this method.
    */
   def stop[T](ref: ActorRef[T], max: FiniteDuration = timeout.duration): Unit = try {
     Await.result(internalSystem ? { x: ActorRef[ActorTestKitGuardian.Ack.type] ⇒ ActorTestKitGuardian.StopActor(ref, x) }, max)

akka-docs/src/main/paradox/typed/testing.md

@@ -211,6 +211,8 @@ Scala
 Java
 :  @@snip [AsyncTestingExampleTest.java](/akka-actor-testkit-typed/src/test/java/jdocs/akka/actor/testkit/typed/javadsl/AsyncTestingExampleTest.java) { #test-stop-actors }
 
+The `stop` method can only be used for actors that were spawned by the same `ActorTestKit`. Other actors
+will not be stopped by that method.
 
 ### Test framework integration