NUnit Extensibility - Get failure messages

I have been searching for some time for ways to get the error message in NUnit. So far, I found some classes that use IAddin and EventListener to get the message, but it didn't work. I based this code on this links:

About extensions

Source code

Extensability

I added the code to the project, but nothing is being recorded, or being done when the tests failed. I read that I have to add the dll to some "NUnit\addins\" folder, but I couldn't find any addin folder with this "addins".

I don't know what I'm missing, can someone help me?

Below is the code that I used:

using System;
using System.IO;
using NUnit.Core;
using NUnit.Core.Extensibility;

namespace Test
{
    [NUnitAddinAttribute(Type = ExtensionType.Core,
                         Name = "Database Addin",
                         Description = "Writes test results to the database.")]
    public class MyNunitExtension : IAddin, EventListener
    {
        public bool Install(IExtensionHost host)
        {
            IExtensionPoint listeners = host.GetExtensionPoint("EventListeners");
            if (listeners == null)
                return false;

        listeners.Install(this);
        return true;
    }

    public void RunStarted(string name, int testCount) { }
    public void RunFinished(TestResult result) { }
    public void RunFinished(Exception exception) { }
    public void TestStarted(TestName testName) { }

    public void TestFinished(TestResult result)
    {
        using (var arq = File.Open(@"C:\Temp\Log.txt", FileMode.Append))
        using (var writer = new StreamWriter(arq))
        {
            var message = string.Format("[{0:s}] [{1}] {2}", DateTime.Now,
                result.ResultState, result.Name);
            writer.WriteLine(message);
            var isFailure =
                result.ResultState == ResultState.Error ||
                result.ResultState == ResultState.Failure;
            if (isFailure)
            {
                writer.WriteLine(result.Message);
            }
        }
    }

    public void SuiteStarted(TestName testName) { }
    public void SuiteFinished(TestResult result) { }
    public void UnhandledException(Exception exception) { }
    public void TestOutput(TestOutput testOutput) { }
}
}