/// <summary>
        /// Write the actual value for a failing constraint test to a
        /// MessageWriter. Overriden to write additional information 
        /// in the case of an Exception.
        /// </summary>
        /// <param name="writer">The MessageWriter to use</param>
        public override void WriteActualValueTo(MessageWriter writer)
        {
            Exception ex = actual as Exception;
            base.WriteActualValueTo(writer);

            if (ex != null)
            {
                writer.WriteLine(" ({0})", ex.Message);
                writer.Write(ex.StackTrace);
            }
        }