// Get necessary fields.
Field field = Client.class.getDeclaredField("callbackPollers");
field.setAccessible(true);
Map callbackPollers = (Map) field.get(client);
assertEquals(1, callbackPollers.size());
CallbackPoller poller = (CallbackPoller) callbackPollers.values().iterator().next();
field.setAccessible(true);
Class[] classes = CallbackPoller.class.getDeclaredClasses();
Class handleThreadClass = null;
Class acknowledgeThreadClass = null;
for (int i = 0; i < classes.length; i++)