How to set up an email or notification service for asp.net mvc

Question

How do I create an email sending notification service class that I can mock and unit test?

My service is in another layer which is a class library. I'm trying not to import the smtp client, but if this is unavoidable, then its no problem. This is what I have now:

public class EmailNotificationService : INotificationService
{
    private readonly EmailNotification _emailNotification;

    public EmailNotificationService(EmailNotification emailNotification)
    {
        _emailNotification = emailNotification;
    }

    public void Notify()
    {
        using (var mail = new MailMessage())
        {
            //If no replyto was passed in the notification, then make it null.
            mail.ReplyTo = string.IsNullOrEmpty(_emailNotification.ReplyTo) ? null : new MailAddress(_emailNotification.ReplyTo);

            mail.To.Add(_emailNotification.To);
            mail.From = _emailNotification.From;
            mail.Subject = _emailNotification.Subject;
            mail.Body = _emailNotification.Body;
            mail.IsBodyHtml = true;

            //this doesn't seem right.
            SmtpClient client = new SmtpClient();
            client.Send(mail);
        }
    }
}

public class EmailNotification
{
    public EmailNotification()
    {
        To = "";
        ReplyTo = "";
        Subject = "";
        Body = "";
    }
    public string To { get; set; }
    public string ReplyTo { get; set; }
    public string Subject { get; set; }
    public string Body { get; set; }

}

Answer 1

If you don't want to import the System.Net.Mail library, you would have to use an interface. Note that this doesn't really help much for your unit testing though

public interface IEmailSender{
     void Send(EmailNotification emailNotification);
}

and then in your EmailNotificationService class you can add the following property or pass in the IEmailSender in your constructor

private IEmailSender emailSender;

public IEmailSender EmailSender
{
     get{
          if(this.emailSender == null){
               //Initialize new EmailSender using either
               // a factory pattern or inject using IOC 
          }
          return this.emailSender
     }
     set{
          this.emailSender = value;
     }
}

your Notify method would become

public void Notify()
{
    EmailSender.Send(_emailNotification);
}

you would then create a concrete class that implements the IEmailSender interface

public class MyEmailSender: IEmailSender
{
     public void Send(EmailNotification emailNotification)
     {
        using (var mail = new MailMessage())
        {
            //If no replyto was passed in the notification, then make it null.
            mail.ReplyTo = 
                    string.IsNullOrEmpty(_emailNotification.ReplyTo) ? null : 
                    new MailAddress(_emailNotification.ReplyTo);

            mail.To.Add(emailNotification.To);
            mail.From = emailNotification.From;
            mail.Subject = emailNotification.Subject;
            mail.Body = emailNotification.Body;
            mail.IsBodyHtml = true;

            SmtpClient client = new SmtpClient();
            client.Send(mail);
        }
     }
}