Merge pull request #24070 from akka/wip-SendQueueSpec-patriknw

additional test of SendQueue

akka-remote/src/test/scala/akka/remote/artery/SendQueueSpec.scala

@@ -13,6 +13,7 @@ import akka.stream.ActorMaterializer
 import akka.stream.ActorMaterializerSettings
 import akka.stream.scaladsl.Keep
 import akka.stream.scaladsl.Source
+import akka.stream.testkit.TestSubscriber
 import akka.stream.testkit.scaladsl.TestSink
 import akka.testkit.AkkaSpec
 import akka.testkit.ImplicitSender
@@ -147,6 +148,67 @@ class SendQueueSpec extends AkkaSpec("akka.actor.serialize-messages = off") with
       downstream.cancel()
     }
 
+    "deliver first message" in {
+
+      def test(f: (ManyToOneConcurrentArrayQueue[String], SendQueue.QueueValue[String], TestSubscriber.Probe[String]) ⇒ Unit): Unit = {
+
+        (1 to 100).foreach { n ⇒
+          val queue = new ManyToOneConcurrentArrayQueue[String](16)
+          val (sendQueue, downstream) = Source.fromGraph(new SendQueue[String])
+            .toMat(TestSink.probe)(Keep.both).run()
+
+          f(queue, sendQueue, downstream)
+          downstream.expectNext("a")
+
+          sendQueue.offer("b")
+          downstream.expectNext("b")
+          sendQueue.offer("c")
+          sendQueue.offer("d")
+          downstream.expectNext("c")
+          downstream.expectNext("d")
+          downstream.cancel()
+        }
+      }
+
+      test { (queue, sendQueue, downstream) ⇒
+        queue.offer("a")
+        downstream.request(10)
+        sendQueue.inject(queue)
+      }
+      test { (queue, sendQueue, downstream) ⇒
+        sendQueue.inject(queue)
+        queue.offer("a")
+        downstream.request(10)
+      }
+
+      test { (queue, sendQueue, downstream) ⇒
+        queue.offer("a")
+        sendQueue.inject(queue)
+        downstream.request(10)
+      }
+      test { (queue, sendQueue, downstream) ⇒
+        downstream.request(10)
+        queue.offer("a")
+        sendQueue.inject(queue)
+      }
+
+      test { (queue, sendQueue, downstream) ⇒
+        sendQueue.inject(queue)
+        downstream.request(10)
+        sendQueue.offer("a")
+      }
+      test { (queue, sendQueue, downstream) ⇒
+        downstream.request(10)
+        sendQueue.inject(queue)
+        sendQueue.offer("a")
+      }
+      test { (queue, sendQueue, downstream) ⇒
+        sendQueue.inject(queue)
+        sendQueue.offer("a")
+        downstream.request(10)
+      }
+    }
+
   }
 
 }