add unit test protect ExtractEntityId can be shared safely

Related with apache#1463

cluster-sharding/src/test/scala/org/apache/pekko/cluster/sharding/ShardRegionSpec.scala

@@ -18,12 +18,17 @@ import java.io.File
 import com.typesafe.config.ConfigFactory
 import org.apache.commons.io.FileUtils
 import org.apache.pekko
+import org.apache.pekko.Done
+import org.apache.pekko.cluster.sharding.ShardRegion.MessageExtractor
+import org.apache.pekko.stream.scaladsl.{ Sink, Source }
 import pekko.actor.{ Actor, ActorLogging, ActorRef, ActorSystem, PoisonPill, Props }
 import pekko.cluster.{ Cluster, MemberStatus }
 import pekko.cluster.ClusterEvent.CurrentClusterState
 import pekko.testkit.{ DeadLettersFilter, PekkoSpec, TestProbe, WithLogCapturing }
 import pekko.testkit.TestEvent.Mute
 
+import scala.concurrent.{ ExecutionContext, Future }
+
 object ShardRegionSpec {
   val host = "127.0.0.1"
   val tempConfig =
@@ -54,6 +59,7 @@ object ShardRegionSpec {
   val shardTypeName = "Caat"
 
   val numberOfShards = 3
+  val largerShardNum = 20
 
   val extractEntityId: ShardRegion.ExtractEntityId = {
     case msg: Int => (msg.toString, msg)
@@ -66,11 +72,37 @@ object ShardRegionSpec {
     case _                           => throw new IllegalArgumentException()
   }
 
+  val messageExtractor: MessageExtractor = new MessageExtractor {
+    override def entityId(message: Any): String = message match {
+      case msg: Int => msg.toString
+      case _        => throw new IllegalArgumentException()
+    }
+
+    override def shardId(message: Any): String = message match {
+      case msg: Int => (msg % largerShardNum).toString
+      case _        => throw new IllegalArgumentException()
+    }
+
+    override def entityMessage(message: Any): Any = message
+  }
+
   class EntityActor extends Actor with ActorLogging {
     override def receive: Receive = {
       case msg => sender() ! msg
     }
   }
+
+  class IDMatcherActor extends Actor with ActorLogging {
+    override def receive: Receive = {
+      case msg =>
+        val selfEntityId = self.path.name
+        val msgEntityId = messageExtractor.entityId(msg)
+        if (selfEntityId != msgEntityId) {
+          throw new IllegalStateException(s"EntityId mismatch: $selfEntityId != $msgEntityId")
+        }
+        sender() ! msg
+    }
+  }
 }
 class ShardRegionSpec extends PekkoSpec(ShardRegionSpec.config) with WithLogCapturing {
 
@@ -183,4 +215,43 @@ class ShardRegionSpec extends PekkoSpec(ShardRegionSpec.config) with WithLogCapt
     }
   }
 
+  "ExtractEntityId" must {
+    "can be safely share to multiple shards" in {
+      implicit val ec: ExecutionContext = system.dispatcher
+
+      Cluster(sysA).join(Cluster(sysA).selfAddress) // coordinator on A
+      awaitAssert(Cluster(sysA).selfMember.status shouldEqual MemberStatus.Up, 1.second)
+
+      within(10.seconds) {
+        awaitAssert {
+          Set(sysA).foreach { s =>
+            Cluster(s).sendCurrentClusterState(testActor)
+            expectMsgType[CurrentClusterState].members.size shouldEqual 2
+          }
+        }
+      }
+
+      val shardTypeName = "Doog"
+      val region = ClusterSharding(sysA).start(
+        shardTypeName,
+        Props[IDMatcherActor](),
+        ClusterShardingSettings(system),
+        messageExtractor)
+
+      val total = largerShardNum * 100
+      val source = Source(1 to total)
+
+      val flow = source.mapAsync(parallelism = largerShardNum) { i =>
+        Future {
+          region.tell(i, p1.ref)
+        }
+      }
+
+      val result = flow.runWith(Sink.ignore)
+
+      result.futureValue shouldEqual Done
+      p1.receiveN(total, 10.seconds)
+    }
+  }
+
 }