log4net appender for xunit output. credit: http://stackoverflow.com/a/29907379/487544

TestOutputAppender.cs

    using log4net.Appender;
    using log4net.Core;
    using log4net.Layout;

    using Xunit.Abstractions;

    public class TestOutputAppender : AppenderSkeleton
    {
        private readonly ITestOutputHelper _xunitTestOutputHelper;

        public TestOutputAppender(ITestOutputHelper xunitTestOutputHelper)
        {
            this._xunitTestOutputHelper = xunitTestOutputHelper;
            this.Name = "TestOutputAppender";
            this.Layout = new PatternLayout("%date [%thread] %-5level %logger - %message");
        }

        protected override void Append(LoggingEvent loggingEvent)
        {
            this._xunitTestOutputHelper.WriteLine(this.RenderLoggingEvent(loggingEvent));
        }
    }
    
    /*
        // Wire up in test class's constructor:
        public MyTestClass(ITestOutputHelper output)
        {
            BasicConfigurator.Configure(new TestOutputAppender(output));
        }
    */