private Integer createServerCache(Boolean isListenerPresent) throws IOException {
    createCache(new Properties());
    AttributesFactory factory = new AttributesFactory();
    factory.setScope(Scope.DISTRIBUTED_ACK);
    factory.setDataPolicy(DataPolicy.REPLICATE);
    if (isListenerPresent == true) {
      CacheListener serverListener = new HAServerListener();
      factory.setCacheListener(serverListener);
    }
    RegionAttributes attrs = factory.create();
    cache.createRegion(REGION_NAME, attrs);
    CacheServerImpl server = (CacheServerImpl) cache.addCacheServer();
    assertNotNull(server);
    int port = getRandomAvailableTCPPort();
    server.setPort(port);
    server.setNotifyBySubscription(true);
    server.start();
    return server.getPort();
  }
This is to test the serialization mechanism of ClientUpdateMessage. Added after CQ support.
This could be done in different way, by overflowing the HARegion queue.
geode-cq/src/distributedTest/java/org/apache/geode/internal/cache/ha/HADispatcherDistributedTest.java