Enforce valid seqnr for deletes, #25487 (#25488)

akka-persistence/src/test/scala/akka/persistence/PersistentActorSpec.scala

@@ -78,6 +78,9 @@ object PersistentActorSpec {
       case d: DeleteMessagesSuccess ⇒
         val replyTo = askedForDelete.getOrElse(throw new RuntimeException("Received DeleteMessagesSuccess without anyone asking for delete!"))
         replyTo ! d
+      case d: DeleteMessagesFailure ⇒
+        val replyTo = askedForDelete.getOrElse(throw new RuntimeException("Received DeleteMessagesFailure without anyone asking for delete!"))
+        replyTo ! d
     }
 
     override protected def onPersistRejected(cause: Throwable, event: Any, seqNr: Long): Unit =
@@ -1538,6 +1541,18 @@ abstract class PersistentActorSpec(config: Config) extends PersistenceSpec(confi
       expectMsg(Nil)
     }
 
+    "not be able to delete higher seqnr than current" in {
+      val persistentActor = behavior1PersistentActor
+      persistentActor ! Cmd("b")
+      persistentActor ! GetState
+      expectMsg(List("a-1", "a-2", "b-1", "b-2"))
+      persistentActor ! Delete(5L) // > current 4
+      persistentActor ! "boom" // restart, recover
+      expectMsgType[DeleteMessagesFailure].cause.getMessage should include("less than or equal to lastSequenceNr")
+      persistentActor ! GetState
+      expectMsg(List("a-1", "a-2", "b-1", "b-2"))
+    }
+
     "recover the message which caused the restart" in {
       val persistentActor = recoverMessageCausedRestart
       persistentActor ! "Boom"