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:

• Avalonia.Headless.NUnit which also includes Avalonia.
• Avalonia.Themes.Fluent as even headless controls need a theme

подсказка

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);
    }
}

примечание

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.