Test code to show non-thread-safety of List<>

ConcurrentListAddTest.cs

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

namespace Tests {
    [TestFixture]
    public class ConcurrentListAddTest {
        [Test]
        public void Should_eventually_throw_exception() {
            var r = new Random();
            var list = new List<object>();
            try {
                while (true) {
                    var tasks = Enumerable
                        .Range(1, 5)
                        .Select(i => Task.Run(async () => {
                            list.Add(new object());
                            await Task.Delay(r.Next(75, 125));
                            list.Add(new object());
                            await Task.Delay(r.Next(75, 125));
                            list.Add(new object());
                            list.Add(new object());
                            await Task.Delay(r.Next(75, 125));
                            list.Add(new object());
                            list.Add(new object());
                            list.Add(new object());
                            await Task.Delay(r.Next(75, 125));
                            list.Add(new object());
                        })).ToArray();
                    Task.WaitAll(tasks);

                    if (list.Any(o => o == null))
                        throw new NullReferenceException();
                }
            }
            catch (AggregateException ex) {
                var exes = string.Join(", ", ex.InnerExceptions.Select(e => e.GetType().Name).Distinct());
                Console.WriteLine("Caught {0}", exes);
            }
            catch (NullReferenceException) {
                Console.WriteLine("Caught NullReferenceException");
            }
        }
    }
}