TestCallbackHandler callbackHandler = new TestCallbackHandler();
client.addListener(callbackHandler, new HashMap());
log.info("First callback handler is installed.");
// Reinstall callback handler. Test passes if no exception is thrown.
client.removeListener(callbackHandler);
Thread.sleep(waitPeriod);
client.addListener(callbackHandler, new HashMap());
log.info("Second callback handler is installed.");
client.removeListener(callbackHandler);