### Question:
ButtonWithProgressVM extends SimpleButtonVM implements ProgressButtonVM { @Override public void showLoading() { loading = true; notifyShowProgress(); } ButtonWithProgressVM(int layoutId, boolean enabled, int clickableResId,
			int[] enableDisableResIds, ButtonCommand actionCommand, int imageViewId,
			int progressBarId); @Override void showLoading(); @Override void closeLoading(); @Override int getProgress(); @Override int getImage(); @Override boolean isLoading();  }### Answer:
@Test public void shouldNotifyButtonVMListener() { ButtonWithProgressVM buttonWithProgressVM = (ButtonWithProgressVM) buttonVM; buttonWithProgressVM.registerListener(mockedButtonVMListener); buttonWithProgressVM.showLoading(); verify(mockedButtonVMListener).onProgressValueChanged(true, buttonWithProgressVM); }