### Question:
RemitSyncExecutor implements Handler.Callback { public void postRemoveFreeId(int id) { final Message message = handler.obtainMessage(WHAT_REMOVE_FREE_ID); message.arg1 = id; handler.sendMessage(message); } RemitSyncExecutor(@NonNull RemitAgent agent);   RemitSyncExecutor(@NonNull RemitAgent agent, @Nullable Handler handler,
                      @NonNull Set<Integer> freeToDBIdList); void postSyncInfoDelay(int id, long delayMillis); void postSync(int id); void postSync(List<Integer> idList); void postRemoveInfo(int id); void postRemoveFreeIds(List<Integer> idList); void postRemoveFreeId(int id); boolean handleMessage(Message msg);  }### Answer:
@Test public void postRemoveFreeId() { executor.postRemoveFreeId(1); verify(handler).sendMessage(messageCaptor.capture()); final Message message = messageCaptor.getValue(); assertThat(message.arg1).isEqualTo(1); assertThat(message.what).isEqualTo(WHAT_REMOVE_FREE_ID); }