### Question:
DecisionNavigatorObserver { void onNestedElementSelected(final @Observes EditExpressionEvent event) { getOptionalPresenter().ifPresent(DecisionNavigatorPresenter::refresh); }  void init(final DecisionNavigatorPresenter presenter);  }### Answer:
@Test public void testOnNestedElementSelected() { observer.init(presenter); observer.onNestedElementSelected(new EditExpressionEvent(clientSession, uuid, hasExpression, Optional.of(hasName), false)); verify(presenter).refresh(); }