public void WhenShowParentWindow_ItActivates() { //Arrange var eventAggregator = Mock.Create<IEventAggregator>(Behavior.Loose); var mainVM = new MainViewModel { EventAggregator = eventAggregator }; var parentWindow = new BaseTopLevelWindow(); var childWindow = Mock.Create<ITopLevelWindow>(Behavior.Loose); Mock.Arrange(() => childWindow.Breadcrumbs).Returns(new ObservableCollection<IBreadcrumbItem>()); mainVM.Windows.Add(parentWindow); mainVM.ShowChildWindow(parentWindow, childWindow); // Act mainVM.ShowParentWindow(parentWindow); //Assert Assert.AreEqual(parentWindow, mainVM.SelectedWindow); }