Test to check the speed of List.ForEach vs List.AddRange

Benchmark.cs

using System;
using System.Collections.Generic;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Attributes.Jobs;

namespace ForEachVsAddRange
{
    [MemoryDiagnoser]
    public class Benchmark
    {
        private List<string> _list;
        private List<string> _toAdd;

        private const int Loops = 1000;

        private readonly Random _rand = new Random(42);

        [Params(100, 1000, 10000)]
        public int ListSize { get; set; }

        [Setup]
        public void Setup()
        {
            _list = new List<string>(Loops * ListSize);
            _toAdd = new List<string>(ListSize);

            for (var i = 0; i < ListSize; i++)
            {
                _toAdd.Add(new string('=', _rand.Next(1, 10000)));
            }
        }

        [Benchmark(Baseline = true)]
        public void ClassicLoop()
        {
            _list.Clear();

            for (var i = 0; i < Loops; i++)
            {
                for (var j = 0; j < ListSize; j++)
                {
                    _list.Add(_toAdd[j]);
                }
            }
        }

        [Benchmark]
        public void ForEach()
        {
            _list.Clear();

            for (var i = 0; i < Loops; i++)
            {
                _toAdd.ForEach(_list.Add);
            }
        }

        [Benchmark]
        public void AddRange()
        {
            _list.Clear();

            for (var i = 0; i < Loops; i++)
            {
                _list.AddRange(_toAdd);
            }
        }
    }
}

Program.cs

using BenchmarkDotNet.Running;

namespace ForEachVsAddRange
{
    class Program
    {
        static void Main(string[] args)
        {
            BenchmarkRunner.Run<Benchmark>();
        }
    }
}