Add user to the group in SharePoint 2010 using Client Object Model

using System; using System.Collections.Generic; using System.Linq; using System.Text; using Microsoft.SharePoint.Client;   namespace COM {     class Program     {         static void Main(string[] args)         {             // siteURL is the string that contains the site URL             string siteUrl = "http://serverName:50000/sites/Testing";             // ClientContext object is used to get the context for the SharePoint objects             ClientContext clientContext = new ClientContext(siteUrl);             Web web = clientContext.Web;             User user = web.EnsureUser(@"domainName\userName");             Group testingOwnersGroup = web.SiteGroups.GetById(6);             UserCollection userCollection = testingOwnersGroup.Users;             userCollection.AddUser(user);             clientContext.Load(userCollection);                           clientContext.ExecuteQuery();                    }     } }