How to get a `ITestOutputHelper` in a `IClassFixture`?

Question

Using xUnit with asp.net, I have isolated some test dependencies in different fixtures that should be global (they perform test setup that can be shared among multiple tests); but on more than one occasion I needed to write some logs on those fixtures to debug certain situations.

A sample is:

public class UnitTest(InterestingFixture f): IClassFixture<InterestingFixture> {
    [Fact]
    public void Test() {
       var data = f.GetData();
       // do something with data...
    }
}

public class InterestingFixture {
  public InterestingFixture() {
    // performs some initialization which I want to log to the test output
  }
}

In the same above, I want InterestingFixture to get an instance of ITestOutputHelper so that I can write something to the output. I've tried adding ITestOutputHelper to its constructor, but it seems that xUnit isn't injecting anything on the IClassFixtures.

I could manually instantiate InterestingFixture, but it will remove the singleton properties given by xUnit.

How can I accomplish that? Is it supported by xUnit?

I'm on xUnit 2.8.

Answer 1

Not sure if this is exactly what you are trying to accomplish but, your fixture class could store the logs and let your test class print them. Like so:

public class TestFixture : IAsyncLifetime
{
    private readonly StringBuilder _sb = new();
    public string Logs => _sb.ToString();

    public Task InitializeAsync()
    {
        _sb.AppendLine("Initialising...");

        // do something

        _sb.AppendLine("Success!");
        return Task.CompletedTask;
    }

    public Task DisposeAsync() => Task.CompletedTask;
}

public class UnitTest : IClassFixture<TestFixture>
{
    private readonly TestFixture _fixture;
    private readonly ITestOutputHelper _output;

    public UnitTest(TestFixture fixture, ITestOutputHelper output)
    {
        _fixture = fixture;
        _output = output;

        _output.WriteLine(_fixture.Logs);
    }

    [Fact]
    public void Test1()
    {
        // your test
    }
}