### Question:
DecisionNavigatorObserver { void setActiveParent(final EditExpressionEvent event) { getTreePresenter().setActiveParentUUID(event.getNodeUUID()); }  void init(final DecisionNavigatorPresenter presenter);  }### Answer:
@Test public void testSetActiveParent() { final EditExpressionEvent event = makeEditExpressionEvent(); observer.init(presenter); observer.setActiveParent(event); verify(treePresenter).setActiveParentUUID(uuid); }