xUnit tests are not discovered (and run) in a .Net9 UWP application

[vgromfeld]

Description

I've converted an UWP test application using xUnit to .Net 9 + AOT.
The xUnit tests are not discovered (and not run).
See Modernize your UWP app with preview UWP support for .NET 9 and Native AOT for more details

Steps To Reproduce

1. Create an UWP test application
2. Import xUnit nuget package
3. Convert the project to a .Net 9 project
4. Add an MSTest class:

[TestClass]
public class msUnitTest
{
    [TestMethod]
    public void Test()
    {
        var a = 10;
        Assert.AreEqual(10, a);
    }
}

5. Add an xUnit test class

public class xUnitTest
{
    [Fact]
    public void Test()
    {
        var a = 10;
        a.Should().Be(10);
    }
}

6. Run the tests

Only the msTest.Test test is run. The xUnitTest.Test testis not discovered by the test runner and not run.

Expected Behavior

All the tests should run.

Version Info

TargetFramework = net9.0-windows10.0.26100.0
Microsoft.NET.Test.Sdk = 17.14.0-preview-25107-01
MSTest = 3.8.2
xunit = 2.9.3
xunit.runner.visualstudio = 3.0.2

Additional Context

Sample test application: UnitTests.zip

[vgromfeld]

This has initially be opened in the csWinrt project: microsoft/CsWinRT#1943
This issue affects only .NET 9 + UWP test. "Regular" .NET 9 test projects are working fine.
XUnit stops discovering the test once I'm adding <Platforms>x86;x64;arm64</Platforms> to the project.