Skip to main content
Version: 11.0.x

Headless Testing with NUnit

Preparation​

This page assumes that NUnit project was already created. If not, please follow NUnit "Getting Started" and "Installation" here https://docs.nunit.org/articles/nunit/getting-started/installation.html.

Install packages​

Aside from NUnit packages, we need to install two more packages:

tip

Headless platform doesn't require any specific theme, and it is possible to swap FluentTheme with any other.

Setup Application​

As in any other Avalonia app, an Application instance needs to be created, and themes need to be applied. When using the Headless platform, the setup is not much different from a regular Avalonia app and can mostly be reused.

<Application xmlns="https://github.com/avaloniaui"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             x:Class="Tests.App">
  <Application.Styles>
    <FluentTheme />
  </Application.Styles>
</Application>

And the code:

using Avalonia;
using Avalonia.Headless;

public class App : Application
{
    public override void Initialize()
    {
        AvaloniaXamlLoader.Load(this);
    }
}
note

Usually, the BuildAvaloniaApp method is defined in the Program.cs file, but NUnit/XUnit tests don't have it, so it is defined in the App file instead.

Initialize NUnit Tests​

The [AvaloniaTestApplication] attribute wires the tests in the current project with the specific application. It needs to be defined once per project in any file.

[assembly: AvaloniaTestApplication(typeof(TestAppBuilder))]

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

Test Example​

[AvaloniaTest]
public void Should_Type_Text_Into_TextBox()
{
    // Setup controls:
    var textBox = new TextBox();
    var window = new Window { Content = textBox };

    // Open window:
    window.Show();

    // Focus text box:
    textBox.Focus();

    // Simulate text input:
    window.KeyTextInput("Hello World");

    // Assert:
    Assert.AreEqual("Hello World", textBox.Text);
}

Instead of the typical [Test] attribute, we need to use [AvaloniaTest] as it sets up the UI thread. Similarly, instead of [Theory], there is a [AvaloniaTheory] attribute.