Failed ECB Reference

using NUnit.Framework;
using System.Collections;
using System.Collections.Generic;
using Unity.Entities;
using UnityEngine;

namespace ECBEntityRefTests
{
    struct CompA : IComponentData
    {

    }

    class CreateRef : SystemBase
    {
        EndSimulationEntityCommandBufferSystem _barrier;

        protected override void OnCreate()
        {
            base.OnCreate();

            _barrier = World.GetOrCreateSystem<EndSimulationEntityCommandBufferSystem>();
        }

        protected override void OnUpdate()
        {
            var ecb = _barrier.CreateCommandBuffer().ToConcurrent();
            var arch = EntityManager.CreateArchetype(typeof(CompA));
            Entities
                .ForEach((int entityInQueryIndex, Entity e, ref DynamicBuffer<LinkedEntityGroup> group) =>
            {
                var newA = ecb.CreateEntity(entityInQueryIndex, arch);
                group.Add(newA);
            }).ScheduleParallel();
            _barrier.AddJobHandleForProducer(Dependency);
        }
    }

    [TestFixture]
    public class ECBEntityReferenceTests
    {
        [Test]
        public void TestRef()
        {
            DefaultWorldInitialization.Initialize("DefaultWorld", true);

            var world = World.DefaultGameObjectInjectionWorld;
            var em = world.EntityManager;
            
            var refSystem = world.GetOrCreateSystem<CreateRef>();
            var barrier = world.GetOrCreateSystem<EndSimulationEntityCommandBufferSystem>();

            var groupEntity = em.CreateEntity(typeof(LinkedEntityGroup));

            refSystem.Update();
            barrier.Update();

            em.CompleteAllJobs();

            var buffer = em.GetBuffer<LinkedEntityGroup>(groupEntity);
            var aQuery = em.CreateEntityQuery(typeof(CompA));

            Assert.AreEqual(aQuery.GetSingletonEntity(), buffer[0].Value);
        }
    }
}