### Question:
DropBoxManager extends FileSender { public void unLink() { preferenceHelper.setDropBoxAccessKeyName(null); preferenceHelper.setDropBoxOauth1Secret(null); } DropBoxManager(PreferenceHelper preferenceHelper); boolean isLinked(); boolean finishAuthorization(); void startAuthentication(Context context); void unLink(); @Override void uploadFile(List<File> files); @Override boolean isAvailable(); @Override boolean hasUserAllowedAutoSending(); void uploadFile(final String fileName); @Override boolean accept(File dir, String name);  }### Answer:
@Test public void Unlink_WhenCalled_KeyCleared(){ PreferenceHelper pm = mock(PreferenceHelper.class); when(pm.getDropBoxAccessKeyName()).thenReturn("aaaaaa"); DropBoxManager dropBoxManager = new DropBoxManager(pm); dropBoxManager.unLink(); verify(pm).setDropBoxAccessKeyName(null); }