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