### Question:
OperationMonitor { public void removeListener(@NonNull OnChangeListener listener) { checkArgument(listener != null); mListeners.remove(listener); }  @SuppressWarnings("unused") synchronized boolean isStarted(); void addListener(@NonNull OnChangeListener listener); void removeListener(@NonNull OnChangeListener listener);  }### Answer:
@Test public void testRemoveListener() { mMonitor.addListener(mListener); mMonitor.removeListener(mListener); mMonitor.start(); mListener.assertLastState(false); }