public void PushTwoViewModels()
{
Navigator navigator = new Navigator(NavigationFixture.ServiceProvider);
FirstTestViewModel vm = navigator.BuildViewModel <FirstTestViewModel>();
Assert.NotNull(vm);
navigator.PushViewModelToStack(vm, false);
Assert.IsType <FirstTestViewModel>(navigator.SelectedViewModel);
Assert.False(navigator.NavigationStackNotEmpty);
SecondTestViewModel secondVm = navigator.BuildViewModel <SecondTestViewModel>();
Assert.NotNull(secondVm);
navigator.PushViewModelToStack(secondVm, false);
Assert.IsType <SecondTestViewModel>(navigator.SelectedViewModel);
Assert.True(navigator.NavigationStackNotEmpty);
}