HowToCdOptionsCore 20180201-03.cs

using System;
using System.Diagnostics;
using Microsoft.Azure.WebJobs.Host;

namespace Samples.SampleBizLogic.Tests
{
    public class UnitTestTraceWriter : TraceWriter
    {
        private readonly Action<TraceEvent> _traceAction;

        public UnitTestTraceWriter(TraceLevel level, Action<TraceEvent> traceAction) : base(level)
        {
            _traceAction = traceAction;
        }

        public override void Trace(TraceEvent traceEvent)
        {
            _traceAction?.Invoke(traceEvent);
        }
    }
}

// ---
using System.Diagnostics;
using Xunit.Abstractions;

namespace Samples.SampleBizLogic.Tests
{ 
    public class UnitTestBase
    {
        public readonly ITestOutputHelper _output;
        private readonly UnitTestTraceWriter _traceWriter;

        public UnitTestBase(ITestOutputHelper output)
        {
            _output = output;

            _traceWriter = new UnitTestTraceWriter(
                TraceLevel.Verbose,
                te => output.WriteLine($"{te}"));
        }
    }
}