XUnit to LibLog Bridge

Bridge.cs

// Simple bridge to allow capturing of LibLog log messages in xUnit 2.0 tests
// Usage:
private readonly ITestOutputHelper _outputHelper;
public Example(ITestOutputHelper outputHelper) { _outputHelper = outputHelper; }
[Test]
public void Test()
{
  using (LogHelper.Capture(_outputHelper, LogProvider.SetCurrentLogProvider))
  {
    // Call library code, log messages will be captured
  }
}

public static class LogHelper
{
    private static readonly XUnitProvider Provider;

    static LogHelper()
    {
        Provider = new XUnitProvider();
    }

    public static IDisposable Capture(ITestOutputHelper outputHelper, Action<ILogProvider> setProvider)
    {
        // TODO Only do this once
        setProvider(Provider);
        
        CallContext.SetData("CurrentOutputHelper", outputHelper);

        return new DelegateDisposable(() =>
        {
            CallContext.SetData("CurrentOutputHelper", null);
        });
    }

    class DelegateDisposable : IDisposable
    {
        private readonly Action _action;

        public DelegateDisposable(Action action)
        {
            _action = action;
        }

        public void Dispose()
        {
            _action();
        }
    }
}

public class XUnitProvider : ILogProvider
{
    public Logger GetLogger(string name)
    {
        return XUnitLogger;
    }

    private bool XUnitLogger(LogLevel logLevel, [CanBeNull] Func<string> messageFunc, [CanBeNull] Exception exception, params object[] formatParameters)
    {
        if (messageFunc == null) return true;
        var currentHelper = (ITestOutputHelper)CallContext.GetData("CurrentOutputHelper");
        if (currentHelper == null)
            return false;

        currentHelper.WriteLine("[{0}] {1}", logLevel, messageFunc());
        if (exception != null)
            currentHelper.WriteLine("Exception:{0}{1}", Environment.NewLine, exception.ToString());

        return true;
    }

    public IDisposable OpenNestedContext(string message)
    {
        throw new NotImplementedException();
    }

    public IDisposable OpenMappedContext(string key, string value)
    {
        throw new NotImplementedException();
    }
}

For the above to work on netcoreapp2.0 or later, need a CallContext shim from http://www.cazzulino.com/callcontext-netstandard-netcore.html