avalonia-testing

Avalonia Testing

Overview

Two testing approaches: ViewModel unit tests (no Avalonia needed, plain xUnit/NUnit), and headless UI tests using Avalonia.Headless (renders without a display).

ViewModel Unit Tests (No UI)

No special setup needed — ViewModels are plain C# classes:

[Fact]
public void Name_Change_RaisesPropertyChanged()
{
    var vm = new MainViewModel();
    var raised = new List<string?>();
    vm.PropertyChanged += (_, e) => raised.Add(e.PropertyName);

    vm.Name = "Alice";

    Assert.Contains(nameof(vm.Name), raised);
    Assert.Equal("Alice", vm.Name);
}

[Fact]
public async Task SaveCommand_WhenNameEmpty_CannotExecute()
{
    var vm = new MainViewModel { Name = "" };
    Assert.False(vm.SaveCommand.CanExecute(null));
}

Headless Testing Setup

NuGet packages:

• Avalonia.Headless
• Avalonia.Headless.XUnit (or .NUnit)

// Assembly-level attribute (AssemblyInfo.cs or top of test file)
[assembly: AvaloniaTestApplication(typeof(TestAppBuilder))]

public class TestAppBuilder
{
    public static AppBuilder BuildAvaloniaApp()
        => AppBuilder.Configure<App>()
            .UseHeadless(new AvaloniaHeadlessOptions { UseHeadlessDrawing = true });
}

Writing Headless Tests (xUnit)

public class MainWindowTests
{
    [AvaloniaFact]
    public void Button_Click_UpdatesViewModel()
    {
        var window = new MainWindow();
        var vm = new MainViewModel();
        window.DataContext = vm;
        window.Show();

        var button = window.FindControl<Button>("SaveButton")!;
        button.RaiseEvent(new RoutedEventArgs(Button.ClickEvent));

        Assert.True(vm.SaveWasCalled);
    }

    [AvaloniaFact]
    public async Task TextBox_Input_UpdatesBinding()
    {
        var window = new MainWindow();
        window.DataContext = new MainViewModel();
        window.Show();

        var textBox = window.FindControl<TextBox>("NameBox")!;
        textBox.RaiseTextInput("Hello");

        await Task.Delay(50); // allow binding to propagate
        Assert.Equal("Hello", ((MainViewModel)window.DataContext!).Name);
    }
}