[1,2,3] から{0 => 1, 1 => 2, 3 => 2} を作りたい in C#

UnitTest1.cs

using System;
using System.Linq;
using System.Collections.Generic;

using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace UnitTestProject1
{
  [TestClass]
  public class UnitTest1
  {
    [TestMethod]
    public void TestMethod1()
    {
      var result = new[] { 1, 2, 3 }
        .Select((x, i) => new[] { i, x })
        .ToDictionary(x => x[0], x => x[1]);

      Assert.AreEqual(1, result[0]);
      Assert.AreEqual(2, result[1]);
      Assert.AreEqual(3, result[2]);
    }
  }
}