GroupBy and SUM using LINQ in C#

public class Test : IEnumerable<Test>
    {
        public string ColName
        {
            get;
            set;
        }

        public int ColVal
        {
            get;
            set;
        }

        #region IEnumerable<Test> Members

        public IEnumerator<Test> GetEnumerator()
        {
            throw new NotImplementedException();
        }

        #endregion

        #region IEnumerable Members

        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
        {
            throw new NotImplementedException();
        }

        #endregion
    }

Code to execute:

List<Test> tests = new List<Test>();

            Test test = new Test();
            test.ColName = "A";
            test.ColVal = 123;
            tests.Add(test);

            test = new Test();
            test.ColName = "A";
            test.ColVal = 10;
            tests.Add(test);

            test = new Test();
            test.ColName = "B";
            test.ColVal = 231;
            tests.Add(test);

            var query1 = from t in tests
                         group t by t.ColName into gr
                         select new
                         {
                             Id = gr.Key,
                             Sum = gr.Sum(r => r.ColVal)
                         };
            foreach (var grp in query1)
            {
                Console.WriteLine("{0}\t{1}", grp.Id, grp.Sum);
            }