如何模拟在单元测试功能中使用的SmtpClient对象

Question

I want to write the Nunit or unit test for the SendMail method which is present in the BatchProcess without sending mails.

How to can I mock the SmtpClient which is present inside another method. Please help.

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            //Assuming we are populating the emails from the data from database
            List<EmailEntity> emails = new List<EmailEntity>();
            BatchProcess.SendMail(emails);
        }
    }

    public class EmailEntity
    {
        public string ToAddress { get; set; }
        public string Subject { get; set; }
        public string Body { get; set; }
    }

    public class BatchProcess
    {
        public static void SendMail(List<EmailEntity> emails)
        {
            foreach (EmailEntity email in emails)
            {
                MailMessage mail = new MailMessage();
                SmtpClient SmtpServer = new SmtpClient("sampleSmtp.sampleTest.com");
                mail.From = new MailAddress("your_email_address@gmail.com");
                mail.To.Add(email.ToAddress);
                mail.Subject = email.Subject;
                mail.Body = email.Body;
                SmtpServer.Port = 587;
                SmtpServer.Credentials = new System.Net.NetworkCredential("username", "password");
                SmtpServer.EnableSsl = true;
                SmtpServer.Send(mail);
            }
        }
    }
}

Answer 1

That's one of the reason why you should use Dependency Injection .

The point is that you shouldn't create an instance of SmtpClient in SendMail() . It's better to define your wrapper over SmtpClient that implements ISmtpClient interface and pass that interface to constructor of BatchProcess so that you could mock it in the test:

public interface ISmtpClient
{
    int Port { get; set; }

    ICredentialsByHost Credentials { get; set; }

    bool EnableSsl { get; set; }

    void Send(MailMessage mail);
}

public class SmtpClientWrapper : SmtpClient, ISmtpClient
{
}

public class BatchProcess
{
    private readonly ISmtpClient smtpClient;

    BatchProcess(ISmtpClient smtpClient)
    {
        this.smtpClient = smtpClient;
    }

    public void SendMail(List<EmailEntity> emails)
    {
        foreach (EmailEntity email in emails)
        {
            MailMessage mail = new MailMessage();
            mail.From = new MailAddress("your_email_address@gmail.com");
            mail.To.Add(email.ToAddress);
            mail.Subject = email.Subject;
            mail.Body = email.Body;

            //  You could leave this configuration here but it's far better to have it configured in SmtpClientWrapper constructor
            //  or at least outside the loop
            smtpClient.Port = 587;
            smtpClient.Credentials = new System.Net.NetworkCredential("username", "password");
            smtpClient.EnableSsl = true;

            smtpClient.Send(mail);
        }
    }
}