Xunit.StaFact | based tests on an STA thread

[UIFact]
public void Navigate_To_Pages()
{
    FrameNavigationWindow window = new();

    var monitor = new ManualResetEventSlim(false);
    window.ViewNavigator.NavigationService.Navigated += (sender, args) => monitor.Set();
    window.ViewNavigator.ContentRendered += (sender, args) => monitor.Set();

    // set content here
    window.ViewNavigator.Content = new PageNoVm1();

    monitor.Wait(TimeSpan.FromSeconds(5));

    // content always null
    Assert.Equal(typeof(PageNoVm1), window.ViewNavigator.Content.GetType());
}

var monitor = new ManualResetEventSlim(false);

window.ViewNavigator.NavigationService.Navigated += (sender, args) => monitor.Set();
window.ViewNavigator.ContentRendered += (sender, args) => monitor.Set();

var page = new PageNoVm1();
window.Dispatcher.Invoke(() => window.ViewNavigator.Content = page);
monitor.Wait(TimeSpan.FromSeconds(3));