Node that joins again should be ignored, see #2184

akka-cluster/src/multi-jvm/scala/akka/cluster/NodeUpSpec.scala

@@ -9,6 +9,8 @@ import akka.remote.testkit.MultiNodeConfig
 import akka.remote.testkit.MultiNodeSpec
 import akka.testkit._
 import akka.util.duration._
+import scala.collection.immutable.SortedSet
+import java.util.concurrent.atomic.AtomicReference
 
 object NodeUpMultiJvmSpec extends MultiNodeConfig {
   val first = role("first")
@@ -33,7 +35,33 @@ abstract class NodeUpSpec
 
       awaitClusterUp(first, second)
 
-      testConductor.enter("after")
+      testConductor.enter("after-1")
+    }
+
+    "be unaffected when joining again" taggedAs LongRunningTest in {
+
+      val unexpected = new AtomicReference[SortedSet[Member]]
+      cluster.registerListener(new MembershipChangeListener {
+        def notify(members: SortedSet[Member]) {
+          if (members.size != 2 || members.exists(_.status != MemberStatus.Up))
+            unexpected.set(members)
+        }
+      })
+      testConductor.enter("listener-registered")
+
+      runOn(second) {
+        cluster.join(node(first).address)
+      }
+      testConductor.enter("joined-again")
+
+      // let it run for a while to make sure that nothing bad happens
+      for (n ← 1 to 20) {
+        100.millis.dilated.sleep()
+        unexpected.get must be(null)
+        cluster.latestGossip.members.forall(_.status == MemberStatus.Up)
+      }
+
+      testConductor.enter("after-2")
     }
   }
 }