tck issue or bug, onSubscribe should be called prior to onComplete always (#24582)

akka-stream-tests-tck/src/test/scala/akka/stream/tck/EmptyProcessorTest.scala

@@ -0,0 +1,32 @@
+/**
+ * Copyright (C) 2014-2018 Lightbend Inc. <https://www.lightbend.com>
+ */
+package akka.stream.tck
+
+import akka.stream.ActorMaterializer
+import akka.stream.scaladsl.Flow
+import org.reactivestreams.Processor
+import org.testng.annotations.Test
+
+class EmptyProcessorTest extends AkkaIdentityProcessorVerification[Int] {
+
+  @Test
+  @throws[Throwable]
+  def reproduce(): Unit = {
+    var i = 0
+    while (i < 100000) {
+      System.out.println("Run " + i)
+      this.required_spec109_mustIssueOnSubscribeForNonNullSubscriber()
+      i += 1
+    }
+  }
+
+  override def createIdentityProcessor(maxBufferSize: Int): Processor[Int, Int] = {
+    implicit val materializer = ActorMaterializer()(system)
+
+    Flow[Int].toProcessor.run()
+  }
+
+  override def createElement(element: Int): Int = element
+
+}