I'm working with visual studio. The solution contains the 4 following projetcs :

DAL

Works with Entity framework + Repository pattern. It contains de DB classes + Repositorys.

BLL

It contains the DTO classes + Services. Services map the DTO classes with the DB classes. It reference the DAL project.

IMessageRepository messageRepo;
    
public MessageService()
{
    this.messageRepo = new MessageRepository();
    AutoMapper.Mapper.Initialize(cfg => cfg.AddProfile<AutoMapperProfile>());
}
    
public MessageService(IMessageRepository repo)
{
    this.messageRepo = repo;
    AutoMapper.Mapper.Initialize(cfg => cfg.AddProfile<AutoMapperProfile>());
}
    
public List<DTO.Message> GetAll()
{
    List<DTO.Message> messages = ((System.Linq.IQueryable<DAL.Message>)messageRepo.GetAll()).ProjectTo<DTO.Message>().ToList();
    return messages;
}

Presentation

It references the BLL project and EntityFramework.SqlServer.dll.

MessageService ms = new MessageService();
List<Message> messages = ms.GetAll();

Bonus : Unit tests

It references the BLL project and the DAL project (It mocks the repositorys)

[TestClass]
public class MessageServiceTest
{
    Mock<IMessageRepository> messageRepo;
    MessageService messageService;

    [TestInitialize]
    public void SetUp()
    {
        // Create a new mock of the repository
        messageRepo = new Mock<IMessageRepository>();

        // Set up the mock for the repository
        messageRepo.Setup(x => x.GetAll()).Returns((new List<DAL.Message>
        {
            new DAL.Message { Id = 1, Content = "Hello world!", Date = DateTime.Now },
            new DAL.Message { Id = 2, Content = "I <3 U!", Date = DateTime.Now }
        }).AsQueryable());

        // Create the service and inject the repository into the service
        messageService = new MessageService(messageRepo.Object);
    }

    [TestMethod]
    public void TestGetAll()
    {
        // Act
        var messages = messageService.GetAll();

        // Assert
        Assert.AreEqual(2, messages.Count, "The messages count is not correct");
    }
}

I'm new to software architecturing. What are your thoughts on this architecture? Any improvements?