@Test(expected = NotAllowedException.class)
public void should_not_allow_to_save_a_new_property_when_property_with_same_name_already_exists() throws Exception {

    Property alreadyAddedProperty = aProperty().build();
    Widget aWidget = addToRepository(aWidget().custom().property(alreadyAddedProperty).build());
    widgetRepository.addProperty(aWidget.getId(), alreadyAddedProperty);
}