NO-JIRA Adding Test to validate clustering distribution under paging

No problems reported on this test.
I needed to validate rather if messages were being distributed correctly when either SNF or the final address itself was paged. Rather than throw away the test I decided to keep the validation here.

tests/integration-tests/src/test/java/org/apache/activemq/artemis/tests/integration/cluster/distribution/PagedSNFTopicDistributionTest.java

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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.activemq.artemis.tests.integration.cluster.distribution;
+
+import javax.jms.Connection;
+import javax.jms.ConnectionFactory;
+import javax.jms.MessageConsumer;
+import javax.jms.MessageProducer;
+import javax.jms.Session;
+import javax.jms.TextMessage;
+import javax.jms.Topic;
+import java.util.HashMap;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import org.apache.activemq.artemis.api.core.RoutingType;
+import org.apache.activemq.artemis.core.persistence.impl.journal.JournalRecordIds;
+import org.apache.activemq.artemis.core.postoffice.impl.LocalQueueBinding;
+import org.apache.activemq.artemis.core.server.cluster.impl.MessageLoadBalancingType;
+import org.apache.activemq.artemis.core.server.impl.AddressInfo;
+import org.apache.activemq.artemis.tests.util.CFUtil;
+import org.junit.Assert;
+import org.junit.Test;
+
+public class PagedSNFTopicDistributionTest extends ClusterTestBase {
+
+   public boolean isNetty() {
+      return true;
+   }
+
+   @Test
+   public void testTopicWhileSNFPaged() throws Exception {
+      final int nmessages = 100;
+      setupServer(0, true, isNetty());
+      setupServer(1, true, isNetty());
+
+      setupClusterConnection("cluster0", "topics", MessageLoadBalancingType.ON_DEMAND, 1, isNetty(), 0, 1);
+      setupClusterConnection("cluster1", "topics", MessageLoadBalancingType.ON_DEMAND, 1, isNetty(), 1, 0);
+
+      startServers(0, 1);
+
+      waitForTopology(servers[0], 2);
+      waitForTopology(servers[1], 2);
+
+      setupSessionFactory(0, isNetty());
+      setupSessionFactory(1, isNetty());
+
+      servers[0].addAddressInfo(new AddressInfo("topics.A").addRoutingType(RoutingType.MULTICAST));
+      servers[1].addAddressInfo(new AddressInfo("topics.A").addRoutingType(RoutingType.MULTICAST));
+
+      ConnectionFactory factoryServer0 = CFUtil.createConnectionFactory("core", "tcp://localhost:61616");
+      ConnectionFactory factoryServer1 = CFUtil.createConnectionFactory("core", "tcp://localhost:61617");
+
+      // creating the subscription on server0
+      try (Connection connection = factoryServer0.createConnection()) {
+         connection.setClientID("server0");
+         Session session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
+         Topic topic = session.createTopic("topics.A");
+         session.createDurableSubscriber(topic, "topic-server0");
+      }
+
+      // creating the subscription on server1
+      try (Connection connection = factoryServer1.createConnection()) {
+         connection.setClientID("server1");
+         Session session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
+         Topic topic = session.createTopic("topics.A");
+         session.createDurableSubscriber(topic, "topic-server1");
+      }
+
+      waitForBindings(0, "topics.A", 1, 0, false);
+      waitForBindings(1, "topics.A", 1, 0, false);
+
+      // making everything to page
+      servers[0].getPostOffice().getAllBindings().forEach(b -> {
+         if (b instanceof LocalQueueBinding) {
+            try {
+               ((LocalQueueBinding) b).getQueue().getPagingStore().startPaging();
+            } catch (Exception e) {
+            }
+         }
+      });
+
+      try (Connection connection = factoryServer0.createConnection()) {
+         Session session = connection.createSession(true, Session.AUTO_ACKNOWLEDGE);
+         Topic topic = session.createTopic("topics.A");
+         MessageProducer producer = session.createProducer(topic);
+         for (int i = 0; i < nmessages; i++) {
+            producer.send(session.createTextMessage("msg " + i));
+         }
+         session.commit();
+      }
+
+      // verifying if everything is actually paged, nothing should be rounted on the journal
+      HashMap<Integer, AtomicInteger> counters =  countJournal(servers[0].getConfiguration());
+      Assert.assertEquals("There are routed messages on the journal", 0, getCounter(JournalRecordIds.ADD_REF, counters));
+      Assert.assertEquals("There are routed messages on the journal", 0, getCounter(JournalRecordIds.ADD_MESSAGE, counters));
+      Assert.assertEquals("There are routed messages on the journal", 0, getCounter(JournalRecordIds.ADD_MESSAGE_PROTOCOL, counters));
+
+      // consume remotely on server1
+      try (Connection connection = factoryServer1.createConnection()) {
+         connection.setClientID("server1");
+         Session session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
+         Topic topic = session.createTopic("topics.A");
+         MessageConsumer consumer = session.createDurableSubscriber(topic, "topic-server1");
+         connection.start();
+         for (int i = 0; i < nmessages; i++) {
+            TextMessage message = (TextMessage) consumer.receive(1000);
+            Assert.assertNotNull(message);
+            Assert.assertEquals("msg " + i, message.getText());
+         }
+      }
+
+      // consume locally (to where the message was sent) on server0
+      try (Connection connection = factoryServer0.createConnection()) {
+         connection.setClientID("server0");
+         Session session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
+         Topic topic = session.createTopic("topics.A");
+         MessageConsumer consumer = session.createDurableSubscriber(topic, "topic-server0");
+         connection.start();
+         for (int i = 0; i < nmessages; i++) {
+            TextMessage message = (TextMessage) consumer.receive(1000);
+            Assert.assertNotNull(message);
+            Assert.assertEquals("msg " + i, message.getText());
+         }
+      }
+
+   }
+
+   private int getCounter(byte typeRecord, HashMap<Integer, AtomicInteger> values) {
+      AtomicInteger value = values.get(Integer.valueOf(typeRecord));
+      if (value == null) {
+         return 0;
+      } else {
+         return value.get();
+      }
+   }
+
+}