private void startServer(Integer port) throws IOException {
    CacheServer server1 = getCache().addCacheServer();
    server1.setPort(port);
    server1.setNotifyBySubscription(true);
    server1.start();
  }
Check to see if a client is connected to an endpoint with a specific port
geode-core/src/distributedTest/java/org/apache/geode/internal/cache/tier/sockets/UpdatePropagationDistributedTest.java