public void VerifyIsolate()
{
var vm = new GrapherViewModel(this.Option, this.Session.Object, this.thingNavigationService.Object, this.panelNavigationService.Object, this.dialogNavigationService.Object, this.pluginSettingService.Object);
Assert.AreEqual(1, vm.GraphElements.Count);
var newTrunk = vm.GraphElements.FirstOrDefault();
Assert.Throws <InvalidOperationException>(() => vm.Isolate(newTrunk));
Assert.AreEqual(1, vm.GraphElements.Count);
}