Two ways to find index of longest string in a collection of strings in C#

FindIndexTest.cs

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

namespace Async.Model.UnitTest
{
    public class FindIndexTest
    {
        public struct LengthAndIndex
        {
            public int CurrentIndex;
            public int MaxLenght;
            public int IndexOfMaxLen;
        }

        public int FindIndexOfLongestItem(IEnumerable<string> items)
        {
            var initialMaxLengthAndIndex = new LengthAndIndex() { CurrentIndex = -1, MaxLenght = -1, IndexOfMaxLen = -1 };

            return items.Aggregate(initialMaxLengthAndIndex, (max, val) =>
            {
                max.CurrentIndex++;
                if (val.Length > max.MaxLenght)
                {
                    max.MaxLenght = val.Length;
                    max.IndexOfMaxLen = max.CurrentIndex;
                }

                return max;
            }, max => max.IndexOfMaxLen);
        }

        [Test]
        public void FindIndexOfLongestElementWorks()
        {
            IList<string> haystack = new List<string>() { "hej", "med", "diiiiiiiiiig", "mand" };

            int indexOfMax = FindIndexOfLongestItem(haystack);

            Assert.That(indexOfMax, Is.EqualTo(2));
        }

        public int FindIndexOfLongestItemAlt(List<string> items)
        {
            int maxLen = items.Max(item => item.Length);
            return items.FindIndex(item => item.Length == maxLen);
        }

        [Test]
        public void AlternativeFindIndexOfLongestElementWorks()
        {
            IList<string> haystack = new List<string>() { "hej", "med", "diiiiiiiiiig", "mand" };

            int indexOfMax = FindIndexOfLongestItem(haystack);

            Assert.That(indexOfMax, Is.EqualTo(2));
        }
    }
}