### Question:
PopupHelper implements HasBusyIndicator { public ErrorCallback<Message> getPopupErrorCallback() { return (message, throwable) -> { showErrorPopup(throwable.getMessage()); return false; }; } @Inject  PopupHelper(final ErrorPopup errorPopup); void showInformationPopup(final String message); void showErrorPopup(final String message); void showErrorPopup(final String message,
                               final String detail); void showYesNoPopup(final String title,
                               final String message,
                               final Command yesCommand,
                               final Command noCommand); @Override void showBusyIndicator(final String message); @Override void hideBusyIndicator(); ErrorCallback<Message> getPopupErrorCallback();  }### Answer:
@Test public void testGetPopupErrorCallback() { Message message = mock(Message.class); popupHelper.getPopupErrorCallback().error(message, new Exception(MESSAGE)); verify(popupHelper, times(1)).showErrorPopup(MESSAGE); }