Headless Avalonia UI testing for xUnit 3.x and 4.x, maintained by Wiesław Šoltés.

ProTest packages Avalonia's headless platform and xUnit integration as a standalone solution, adds an adapter for xUnit 4.x, and builds against official Avalonia NuGet packages. No Avalonia checkout, private feed, or developer signing secret is required.

Read the documentation for setup, headless testing, xUnit integration, input simulation, tree inspection, Appium-style automation, and recording.

ProTest.Avalonia.Headless includes a comprehensive set of testing helpers:

• Mouse, keyboard, touch, and multi-touch simulation.
• Gesture recognizer helpers and scripted gestures.
• Visual and logical tree queries, XPath-like selectors, validation, and comparison.
• An in-process Appium-style driver with locators, actions, and waits.
• Frame capture, image sequences, recording sessions, and optional FFmpeg video conversion.

The source is organized under src/Headless/Avalonia.Headless/Testing. Existing Avalonia.HeadlessTestingFramework, .Appium, and .Recording namespaces are preserved. These APIs ship in the headless package and require no separate HeadlessTestingFramework project reference. The Appium-style API runs in-process; real Appium server testing is documented separately.

Package	NuGet	Purpose	Tested xUnit version	Avalonia version
ProTest.Avalonia.Headless		Headless platform, test sessions, and testing helpers	Framework independent	12.1.4, exact
ProTest.Avalonia.Headless.XUnit.v3		xUnit 3.x adapter	3.2.2	12.1.4, exact
ProTest.Avalonia.Headless.XUnit.v4		xUnit 4.x adapter	4.0.2	12.1.4, exact

All three packages target .NET 8 and .NET 10. The stable release is 12.1.4, aligned with Avalonia 12.1.4. New Avalonia versions require a tested ProTest release because the headless platform uses version-specific internals.

xUnit naming: the xUnit framework's 4.x releases still ship as xunit.v3.* packages and use Xunit / Xunit.v3 namespaces. ProTest's .v4 suffix identifies the adapter for those 4.x releases. The adapters constrain their xUnit dependency to the corresponding major version.

Install one adapter per test project. Both expose the original Avalonia.Headless.XUnit namespace, including [AvaloniaFact] and [AvaloniaTheory]. Adapter projects, assemblies, and packages use matching .v3 and .v4 suffixes. The headless assembly remains Avalonia.Headless. Remove official Avalonia.Headless / Avalonia.Headless.XUnit package references when migrating: ProTest supplies those types and assembly identities. Keep other Avalonia packages, such as themes and Skia, at version 12.1.4.

Create a test project with the following project file. This example uses xUnit 4.x and supports dotnet test with the VSTest runner:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>net10.0</TargetFramework>
    <OutputType>Exe</OutputType>
    <IsTestProject>true</IsTestProject>
    <IsPackable>false</IsPackable>
    <Nullable>enable</Nullable>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="ProTest.Avalonia.Headless.XUnit.v4" Version="12.1.4" />
    <PackageReference Include="xunit.v3.mtp-off" Version="4.0.2" />
    <PackageReference Include="xunit.runner.visualstudio" Version="4.0.1" PrivateAssets="all" />
    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.11.0" />
  </ItemGroup>
</Project>

The mtp-off package supports VSTest on .NET 10 while retaining xUnit's native executable runner. For xUnit 3.x, replace the adapter with ProTest.Avalonia.Headless.XUnit.v3 and set xunit.v3.mtp-off to 3.2.2. Use net8.0 to run on .NET 8. Use reflection-based xUnit packages; xUnit Native AOT packages are not supported by these reflection-based adapters.

Configure the test application in TestAppBuilder.cs:

using Avalonia;
using Avalonia.Headless;

[assembly: AvaloniaTestApplication(typeof(Tests.TestAppBuilder))]

namespace Tests;

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

Use the Avalonia attributes for tests that need the UI thread. Constructors, test bodies, async continuations, and test-class cleanup run through the headless session:

using System.Threading.Tasks;
using Avalonia.Controls;
using Avalonia.Headless;
using Avalonia.Headless.XUnit;
using Avalonia.Threading;
using Xunit;

namespace Tests;

public class EditorTests
{
    [AvaloniaFact]
    public async Task Text_input_updates_the_focused_control()
    {
        var editor = new TextBox();
        var window = new Window { Content = editor };
        window.Show();
        try
        {
            editor.Focus();
            window.KeyTextInput("Hello, ProTest");
            await Task.Yield();

            Assert.True(Dispatcher.UIThread.CheckAccess());
            Assert.Equal("Hello, ProTest", editor.Text);
        }
        finally
        {
            window.Close();
        }
    }

    [AvaloniaTheory]
    [InlineData("first")]
    [InlineData("second")]
    public void Theory_rows_run_on_the_UI_thread(string value)
    {
        Assert.True(Dispatcher.UIThread.CheckAccess());
        Assert.Equal(value, new TextBox { Text = value }.Text);
    }
}

Run the tests:

dotnet test

The default headless drawing backend supports control behavior and input without a display server. Add the same themes your application uses when testing template-dependent behavior.

To use Microsoft Testing Platform with the .NET 10 SDK, replace xunit.v3.mtp-off with xunit.v3.mtp-v2 at the same xUnit version. Keep the ProTest adapter and test application configuration unchanged. Place this global.json in the test project directory or a parent directory (or merge the test section into your existing file):

{
  "test": {
    "runner": "Microsoft.Testing.Platform"
  }
}

From that directory, run:

dotnet test --project YourTests.csproj

This setup works with both the xUnit 3.x and 4.x adapters. You can remove xunit.runner.visualstudio and Microsoft.NET.Test.Sdk if all your tools use MTP. For MTP command-line options, see the official xUnit guide. The repository's package integration tests exercise VSTest, the native xUnit runner, and the .NET 10 SDK's MTP runner separately.

To run ordinary [Fact] and [Theory] methods through Avalonia, add:

using Avalonia.Headless.XUnit;

[assembly: AvaloniaTestFramework]

By default, a fresh application/service scope is created for every test. To share an application for the assembly, add:

using Avalonia.Headless;

[assembly: AvaloniaTestIsolation(AvaloniaTestIsolationLevel.PerAssembly)]

Use per-test isolation when tests mutate global services or application resources. UI work is serialized through the headless session even when xUnit schedules tests in parallel. Normal xUnit tests can coexist with Avalonia-attributed tests when assembly-wide integration is not enabled.

Keep UI initialization in the test-class constructor or InitializeAsync. Class and collection fixtures follow xUnit's own lifetime and do not automatically receive dispatcher affinity.

For real pixel rendering, reference Avalonia.Skia and your theme package at 12.1.4, then configure:

public static AppBuilder BuildAvaloniaApp() =>
    AppBuilder.Configure<Application>()
        .UseSkia()
        .UseHeadless(new AvaloniaHeadlessPlatformOptions
        {
            UseHeadlessDrawing = false
        });

After showing a window, call window.CaptureRenderedFrame() in an Avalonia test to obtain a bitmap. The repository's shared headless tests include rendering, keyboard/mouse/touch input, popup behavior, and session isolation.

The framework-independent ProTest.Avalonia.Headless package also supports explicit sessions:

await using var session = HeadlessUnitTestSession.StartNew(typeof(TestAppBuilder));
bool onUiThread = await session.Dispatch(async () =>
{
    await Task.Yield();
    return Dispatcher.UIThread.CheckAccess();
}, CancellationToken.None);

Dispose sessions from outside their dispatcher thread. Cancellation of queued work prevents its delegate from running. Canceling an incomplete active delegate stops that session, cancels its queue, and shuts down its dispatcher so old UI continuations cannot enter another test. Start a new session after that cancellation. A completed delegate retains its result; cancellation cannot interrupt synchronous code that blocks the UI thread.

The standalone headless project uses Avalonia's supported build opt-in for unstable private APIs and pins its official Avalonia dependencies to [12.1.4]. This selects the implementation assemblies rather than the restricted public reference assemblies.

Internal friend access additionally requires the original Avalonia.Headless assembly name and matching strong-name key. The repository includes Avalonia's publicly distributed build/avalonia.snk and public-key declaration. This key is for assembly identity; it is unrelated to NuGet publishing credentials. Consumer test projects need neither that key nor the private-API build flags.

See Avalonia's private API packaging guidance and source provenance.

Compatible adapter sources live in src/Headless/Avalonia.Headless.XUnit.v3 and are linked into the .v4 project with MSBuild Compile items. Shared attributes, discovery, test-case definitions, and result handling are maintained once; version-specific execution and scheduling code stays in each project. Both adapters keep the same C# namespace and compile into separate assemblies.

Build with the .NET 10 SDK; install the .NET 8 and .NET 10 runtimes to run the full test matrix. Python 3 drives the portable verification script.

python3 scripts/build.py

CI runs on Linux, Windows, and macOS. It builds both target frameworks, executes the headless tests, creates .nupkg and .snupkg files, checks package metadata, and runs separate consumer projects against the packed packages. Consumers are copied outside this checkout and restored using only the local package feed and NuGet.org, with an isolated package cache. Both attribute-based and assembly-wide integration run through the native xUnit runner and VSTest. Separate failure probes verify nonzero exits and exception reporting; ordinary test runs reject failures and runner errors.

Packages are written to artifacts/packages. Publishing uses GitHub OIDC and NuGet trusted publishing. Configure the NuGet policy, GitHub environment, and NUGET_USER variable as described in publishing.md. NuGet gallery ownership is assigned by NuGet.org, not by project metadata.

MIT. Original Avalonia attribution is preserved in NOTICE.md. ProTest is an independent distribution maintained by Wiesław Šoltés.