IsGuid

/// <summary>
/// Converts the string representation of a Guid to its Guid 
/// equivalent. A return value indicates whether the operation 
/// succeeded. 
/// </summary>
/// <param name="s">A string containing a Guid to convert.</param>
/// <param name="result">
/// When this method returns, contains the Guid value equivalent to 
/// the Guid contained in <paramref name="s"/>, if the conversion 
/// succeeded, or <see cref="Guid.Empty"/> if the conversion failed. 
/// The conversion fails if the <paramref name="s"/> parameter is a 
/// <see langword="null" /> reference (<see langword="Nothing" /> in 
/// Visual Basic), or is not of the correct format. 
/// </param>
/// <value>
/// <see langword="true" /> if <paramref name="s"/> was converted 
/// successfully; otherwise, <see langword="false" />.
/// </value>
/// <exception cref="ArgumentNullException">
///        Thrown if <pararef name="s"/> is <see langword="null"/>.
/// </exception>
/// <remarks>
/// Original code at https://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=94072&wa=wsignin1.0#tabs
/// 
/// </remarks>
public static bool IsGuid(this string s)
{
    if (s == null)
        throw new ArgumentNullException("s");

    Regex format = new Regex(
        "^[A-Fa-f0-9]{32}$|" +
        "^({|\\()?[A-Fa-f0-9]{8}-([A-Fa-f0-9]{4}-){3}[A-Fa-f0-9]{12}(}|\\))?$|" +
        "^({)?[0xA-Fa-f0-9]{3,10}(, {0,1}[0xA-Fa-f0-9]{3,6}){2}, {0,1}({)([0xA-Fa-f0-9]{3,4}, {0,1}){7}[0xA-Fa-f0-9]{3,4}(}})$");
    Match match = format.Match(s);

    return match.Success;
}

string s = Guid.NewGuid().ToString();

Assert.IsTrue(s.IsGuid());