HeartbeatExtensionPreparator extends ExtensionPreparator<HeartbeatExtensionMessage> { @Override public void prepareExtensionContent() { LOGGER.debug("Preparing HeartbeatExtensionMessage"); prepareHeartbeatMode(msg); } HeartbeatExtensionPreparator(Chooser chooser, HeartbeatExtensionMessage message,
            HeartbeatExtensionSerializer serializer); @Override void prepareExtensionContent();  }
@Test public void testPrepareExtensionContent() { }