Testing Avalonia Applications

<PackageReference Include="Avalonia.Headless.XUnit" Version="11.*" />
<!-- Add this too if you want screenshots: -->
<PackageReference Include="Avalonia.Skia" Version="11.*" />

// TestAppBuilder.cs — one per test assembly
using Avalonia;
using Avalonia.Headless;

[assembly: AvaloniaTestApplication(typeof(TestAppBuilder))]

public static class TestAppBuilder
{
    public static AppBuilder BuildAvaloniaApp() => AppBuilder
        .Configure<App>()
        .UseHeadless(new AvaloniaHeadlessPlatformOptions
        {
            UseHeadlessDrawing = false   // false => Skia renders, screenshots work
        });
}

public class CheckoutViewTests
{
    [AvaloniaFact]
    public void Entering_a_card_enables_the_pay_button()
    {
        var window = new Window { Content = new CheckoutView { DataContext = new CheckoutViewModel() } };
        window.Show();

        var pay = window.FindControl<Button>("PayButton")!;
        var card = window.FindControl<TextBox>("CardNumber")!;

        Assert.False(pay.IsEnabled);

        card.Text = "4242424242424242";
        Dispatcher.UIThread.RunJobs();      // let bindings and layout settle

        Assert.True(pay.IsEnabled);
    }

    [AvaloniaFact]
    public void Clicking_pay_shows_the_confirmation()
    {
        var window = new Window { Content = new CheckoutView { DataContext = PaidViewModel() } };
        window.Show();

        // Real input, dispatched through the real input pipeline.
        window.KeyPressQwerty(PhysicalKey.Tab, RawInputModifiers.None);
        window.MouseDown(new Point(120, 400), MouseButton.Left);
        window.MouseUp(new Point(120, 400), MouseButton.Left);
        Dispatcher.UIThread.RunJobs();

        var confirmation = window.FindControl<TextBlock>("Confirmation")!;
        Assert.Equal("Order confirmed", confirmation.Text);
    }
}

[AvaloniaFact]
public void The_total_stays_visible_at_a_narrow_width()
{
    var window = new Window { Width = 320, Height = 640, Content = new CheckoutView() };
    window.Show();
    Dispatcher.UIThread.RunJobs();

    var total = window.FindControl<TextBlock>("Total")!;
    var bounds = total.Bounds;

    Assert.True(bounds.Width > 0 && bounds.Height > 0);
    Assert.True(bounds.Right <= window.Width);      // not clipped off the edge
}

[AvaloniaFact]
public void Checkout_matches_the_approved_appearance()
{
    var window = new Window { Width = 800, Height = 600, Content = new CheckoutView() };
    window.Show();
    Dispatcher.UIThread.RunJobs();

    using var frame = window.CaptureRenderedFrame()!;
    frame.Save("artifacts/checkout.png");

    // Compare against a committed baseline with your image-diff library of
    // choice, and publish the diff as a CI artifact on failure.
}

// No UI at all. Microseconds. This is where most of the tests should be.
[Fact]
public void Pay_is_disabled_until_the_card_is_valid()
{
    var vm = new CheckoutViewModel(new StubPaymentService());

    Assert.False(vm.CanPay);
    vm.CardNumber = "4242424242424242";
    Assert.True(vm.CanPay);
}