WebApplicationFactory logging regression with v3.10.0

[markm77]

Hi there,

I have a .NET 9 test project (<Project Sdk="MSTest.Sdk/3.x.y">) which uses a WebApplicationFactory (set up as a fixture in [ClassInitialize]). Logging from the WebApplicationFactory has stopped and I isolated the issue to updating from MSTest v3.9.3 to v3.10.0. Reverting back to v3.9.3 has fixed things.

I have quite a complicated project so before setting out to create a minimal repro I just wanted to ask if there are any obvious reasons for this (I couldn't see anything in the release log).

BR,
Mark

[Youssef1313]

Unfortunately, it's hard to say/guess without a repro. If you can create a minimal repro, that's very much appreciated.

[markm77]

OK, I'll have a go at this next week. Thanks!

[Youssef1313]

@markm77 Were you able to get a minimal repro please? Thanks!

[markm77]

Sorry @Youssef1313 , will try to do this tomorrow!

[markm77]

Still working on this....

[markm77]

Hi @Youssef1313 ,

OK I've got to the bottom of what is happening. This was tough to repro as everything seemed to work in simple cases. However let me go through it.

If I have a simple web app:

var builder = WebApplication.CreateBuilder(args);

var app = builder.Build();

app.MapGet("/", (ILogger<Program> logger) =>
{
    logger.LogWarning("Log message from endpoint");
    return "Endpoint alive";
});

app.Run();

public partial class Program { }

and test with an <Project Sdk="MSTest.Sdk/3.9.3"> project test:

using Microsoft.AspNetCore.Mvc.Testing;

namespace Tests;

[TestClass]
public sealed class MyTestClass
{
    private static WebApplicationFactory<Program> _webApplicationFactory = null!;

    [TestMethod]
    public async Task TestMethod()
    {
        Console.WriteLine("TestMethod: start");
        using var httpClient = _webApplicationFactory.CreateClient();
        var response = await httpClient.GetStringAsync("/");
        Console.WriteLine("TestMethod: finish");
    }

    [ClassInitialize]
    public static void ClassInitialise(TestContext context)
    {
        Console.WriteLine("ClassInitialise: start");
        _webApplicationFactory = new WebApplicationFactory<Program>();
        using var httpClient = _webApplicationFactory.CreateClient(); // When commented out, no problems
        Console.WriteLine("ClassInitialise: finish");
    }

    [ClassCleanup]
    public static void ClassCleanup()
    {
        _webApplicationFactory.Dispose();
    }
}

I get test output:

ClassInitialise: start
ClassInitialise: finish
TestMethod: start
TestMethod: finish
2025-09-09T12:20:43.598Z warn: Program[0]
      => SpanId:9a9d2bc51064edd2, TraceId:d5a26339614df42dd1d8a07e7bc9e041, ParentId:0000000000000000 => RequestPath:/ RequestId:0HNFFJD64SNU7
      Log message from endpoint

And if I use <Project Sdk="MSTest.Sdk/3.10.3"> I get test output

ClassInitialise: start
ClassInitialise: finish
TestMethod: start
TestMethod: finish

where everything after TestMethod: finish is removed.

I have noted by a comment which line in ClassInitialise() causes logging to occur after TestMethod: finish but actually such "delayed logging" also happens in my web app - this is just an example to demonstrate the issue.

Hope this helps clear up what is happening.