### Question:
DecisionNavigatorObserver { void onCanvasElementUpdated(final @Observes CanvasElementUpdatedEvent event) { getOptionalPresenter().ifPresent(DecisionNavigatorPresenter::refresh); }  void init(final DecisionNavigatorPresenter presenter);  }### Answer:
@Test public void testOnCanvasElementUpdated() { observer.init(presenter); observer.onCanvasElementUpdated(new CanvasElementUpdatedEvent(canvasHandler, element)); verify(presenter).refresh(); }