LoggingFuturesCallBack implements FutureCallback<T> { @Override public void onFailure(Throwable e) { LOG.warn(message, e); } LoggingFuturesCallBack(String message, Logger LOG); @Override void onSuccess(T t); @Override void onFailure(Throwable e);  }
@Test public void testOnFailure() throws Exception { callBack.onFailure(new Exception()); }