Multiple CSV strutures with FileHelpers

using System;
using System.Collections.Generic;
using System.Linq;
using FileHelpers;
using NUnit.Framework;

namespace ConsoleApplication8
{
    class Program
    {
        [DelimitedRecord(",")]
        public class Format1
        {
            public string Field1;
            public string Field2;
            public string Field3;
            public string Field4;
        }

        [DelimitedRecord(",")]
        public class Format2
        {
            public string Field1;
            public string Field4;
        }

        static Type CustomSelector(MultiRecordEngine engine, string record)
        {
            // count the separators to determine which format to return
            int separatorCount = record.Count(f => f == ',');
            if (separatorCount == 3) // in Structure 1 there are three separators
                return typeof(Format1);
            else
                return typeof(Format2);
        }

        static void Main(string[] args)
        {
            MultiRecordEngine engine;
            engine = new MultiRecordEngine(typeof(Format1), typeof(Format2));
            engine.RecordSelector = new RecordTypeSelector(CustomSelector);

            /// MultiRecords.txt can contain records either of the form
            ///   Field 1,Field 2,Field 3,Field 4
            /// or of the form
            ///   Field 1,Field 4

            // read file - Normally you would use
            //object[] importedObjects = engine.ReadFile("MultiRecords.txt");
            // but for the sake of example we'll use engine.ReadString() instead

            object[] importedObjects = engine.ReadString(
                @"a,b,c,d" + Environment.NewLine +
                @"a,d");

            foreach (object importedObject in importedObjects)
            {
                if (importedObject is Format1)
                {
                    Format1 format1 = (Format1)importedObject;
                    // process it (for example, check the values)
                    Assert.AreEqual("a", format1.Field1);
                    Assert.AreEqual("b", format1.Field2);
                    Assert.AreEqual("c", format1.Field3);
                    Assert.AreEqual("d", format1.Field4);

                }
                else
                if (importedObject is Format2)
                {
                    Format2 format2 = (Format2)importedObject;
                    // process it (for example, check the values)
                    Assert.AreEqual("a", format2.Field1);
                    Assert.AreEqual("d", format2.Field4);
                }
            }
        }
    }
}