Place your test data next to the test code.

CommentReader.cs

using System;
using System.Diagnostics;
using System.Reflection;
using System.Xml;
using NUnit.Framework;

/// <summary>
/// Written in June 2006 by Lars Thorup, ZeaLake and Sune Gynthersen, BestBrains
/// Description here: http://www.zealake.com/2012/04/15/commentreader-place-your-test-data-next-to-the-test-code/
/// </summary>

public class CommentReader
{
    private static XmlDocument generatedDocumentation = new XmlDocument();
    private static StackFrame callingMethodFrame;

    public static string GetElement(string elementName)
    {
        StackTrace stackTrace = new StackTrace();
        callingMethodFrame = stackTrace.GetFrame(1);

        generatedDocumentation.Load(String.Format("{0}.xml",
          Assembly.GetCallingAssembly().FullName.Split(',')[0]));

        XmlNode node = generatedDocumentation.SelectSingleNode(
          String.Format("doc/members/member[contains(@name, '{0}.{1}')]/{2}",
          callingMethodFrame.GetMethod().DeclaringType.ToString(),
          callingMethodFrame.GetMethod().Name,
          elementName));

        if (node != null)
            return node.InnerXml;
        else
            throw new ApplicationException(String.Format("Element '{0}' not found.", elementName));
    }
}

[TestFixture]
public class CommentReaderTest
{
    /// <sample>
    ///    <book>
    ///      <isbn>1234-1234</isbn>
    ///      <title>Code Complete</title>
    ///    </book>
    /// </sample>
    [Test]
    public void TestXmlComment()
    {
        string content = CommentReader.GetElement("sample");

        XmlDocument document = new XmlDocument();
        document.LoadXml(content);
        Assert.AreEqual(@"Code Complete", document.SelectSingleNode("//book/title").InnerText);
    }

    /// <sample>
    ///    create table Orders ( id int, customer int );
    /// </sample>
    [Test]
    public void TestNonXmlComment()
    {
        string content = CommentReader.GetElement("sample");
        Assert.AreEqual(@"create table Orders ( id int, customer int );", content.Trim());
    }

    /// <sample>
    ///    link
    /// </sample>
    [Test]
    public void TestMissingElement()
    {
        try
        {
            CommentReader.GetElement("missing");
            Assert.Fail();
        }
        catch (ApplicationException ex)
        {
            Assert.That(ex.Message, Is.EqualTo("Element 'missing' not found."));
        }
    }
}