Looking up items in HashTable/Dictionary objects that have multiple keys

using System;
using System.Collections.Generic;
using System.Text;

using NUnit.Framework;
using Utility;
using System.Diagnostics;

namespace Testing
{
    [TestFixture]
    public class TestStringDictionaryOnly
    {
        /// <summary>
        /// Define test class to use key for
        /// </summary>
        public class TestClass
        {
            public string Column1 = null;
            public string Column2 = null;

            public TestClass(string Column1, string Column2)
            {
                this.Column1 = Column1;
                this.Column2 = Column2;
            }
        }

        //null keys are a problem that would have to be thought about on every usage
        //dictionary objects need to be created for each additional key

        public class PerfResults { public long initMS; public long lookupMS; }

        private string GetTestClassKey(TestClass testClass)
        {
            return testClass.Column1 + "~" + testClass.Column2;
        }

        public PerfResults GetTestPerf()
        {
            Dictionary<string, TestClass> testLookups = new Dictionary<string, TestClass>();
            Stopwatch stopWatch = new Stopwatch();
            PerfResults results = new PerfResults();

            //test initialization
            stopWatch.Start();
            for (int i = 0; i < 1000000; i++)
            {
                TestClass testClass = new TestClass("Column1-" + i, "Column2-" + i);
                testLookups.Add(GetTestClassKey(testClass), testClass);
            }
            stopWatch.Stop();

            results.initMS = stopWatch.ElapsedMilliseconds;

            //test getting
            stopWatch = new Stopwatch();
            stopWatch.Start();
            for (int i = 0; i < 1000000; i++)
            {
                TestClass testClass = new TestClass("Column1-" + i, "Column2-" + i);
                
                if (!testLookups.ContainsKey(GetTestClassKey(testClass)))
                    throw new ArgumentException("Can't find object we know is there");
            }
            stopWatch.Stop();

            results.lookupMS = stopWatch.ElapsedMilliseconds;

            return results;
        }

        [Test]
        public void TestPerf()
        {
            int testRuns = 10;
            PerfResults totalResults = new PerfResults();

            for (int i = 0; i < testRuns; i++)
            {
                PerfResults thisResult = GetTestPerf();
                totalResults.initMS += thisResult.initMS;
                totalResults.lookupMS += thisResult.lookupMS;
            }

            Debug.WriteLine("Initialization: " + (totalResults.initMS / testRuns).ToString("N0") + "ms");
            Debug.WriteLine("Lookups: " + (totalResults.lookupMS / testRuns).ToString("N0") + "ms");
        }


    }
}