//////////////////////////////////
// Example without dependency
// injection
//////////////////////////////////

public class UserService : IUserService
{
    readonly IRepository<User> _userRepo;
    readonly IEmailService _emailService;

    public UserService()
    {
        _userRepo = new Repository<User>(Configuration.ConnectionStrings["ConnectionStr"]);
        _emailService = new SmtpEmailService(
            Configuration.AppSettings["emailHost"],
            Configuration.AppSettings["emailUser"],
            Configuration.AppSettings["emailPass"],
            Configuration.AppSettings["emailFromAddress"]
        );
    }

    public void AddUser(User user)
    {
        _userRepo.Add(user);

        string subject = "Account created";
        string body = "Thank you, #{0}. Your user account has been created.";
        _emailService.SendEmail(subject, body, user.Email);
    }
}

///////////////////////////////////////
// Solution that lets dependencies
// get injected, instead of constructing
// them in the constructor
////////////////////////////////////////

public class UserService : IUserService
{
    readonly IRepository<User> _userRepo;
    readonly IEmailService _emailService;

    public UserService(IRepository<User> userRepo, IEmailService emailService)
    {
      _userRepo = userRepo;
      _emailService = emailService;
    }

    public void AddUser(User user)
    {
        _userRepo.Add(user);

        string subject = "Account created";
        string body = "Thank you, #{0}. Your user account has been created.";
        _emailService.SendEmail(subject, body, user.Email);
    }
}

//////////////////////////////////////////////////////
// Testing the second example. Testing the first
// example will be nearly impossible, since it
// has hard dependencies on the services it requires
//////////////////////////////////////////////////////

public class MockEmailService : IEmailService
{
    readonly IList<Email> _sentEmails = new List<Email>();

    public void SendEmail(string subject, string body, string recipient)
    {
        var email = new Email
        {
            Subject = subject,
            Body = body,
            Recipient = recipient
        };

        _sentEmails.Add(email);
    }

    public IList<Email> SentEmails
    {
        get { return _sentEmails; }
    }
}

public class MockUserRepository : IRepository<User>
{
    readonly IList<User> _addedUsers = new List<User>();

    public void Add(User user)
    {
        _addedUsers.Add(user);
    }

    public IList<User> AddedUsers
    {
        get { return _addedUsers; }
    }
}

public class UserServiceTest : UnitTest
{
    public void TestAddUser()
    {
        var emailMock = new MockEmailService();
        var repoMock = new MockUserRepository();
        IUserService userService = new UserService(repoMock, emailMock);
        User user = new User
        {
            Username = "metallic",
            Password = "It's a secret",
            Email = "metallic@example.com"
        }
        userService.AddUser(user);

        Assert.AreEqual(repoMock.AddedUsers.Count, 1);
        Assert.AreEqual(emailMock.SentEmails, 1);
    }
}