使用SmtpClient发送Email时，我们可以创建ISmtpClient接口和SmtpClientWrapper适配类，在单元测试中对ISmtpClient进行Mock或自定义FackeSmtpClient，但nDumbster的Facke SMTP Server给我们提供了更直观更简单的方式进行单元测试。可以通过Nuget搜索nDumbster，这里使用的是netDumbster。

1.IEmailSender接口

public interface IEmailSender
{
    void SendMail(string from, string to, string subject, string body);
}

2.SMTPAdapter实现类

public interfacepublic class SMTPAdapter : IEmailSender
{
    public void SendMail(string from, string to, string subject, string body)
    {
        var message = new MailMessage();
        message.IsBodyHtml = true;
        message.From = new MailAddress(from);
        message.To.Add(new MailAddress(to));
        message.Subject = subject;
        message.Body = body;
        using (var smtpClient = new SmtpClient())
        {
            if (smtpClient.Host == null)
            {
                smtpClient.Host = "localhost";
            }
            smtpClient.Send(message);
        }
    }
}

3.使用nDumbster单元测试

public class SMTPAdapterTest
{
    [Fact]
    public void SendMailTest()
    {
        SimpleSmtpServer server = SimpleSmtpServer.Start(25);
        IEmailSender sender = new SMTPAdapter();
        sender.SendMail("[email protected]", "[email protected]", "subject", "body");
        Assert.Equal(1, server.ReceivedEmailCount);
        SmtpMessage mail = (SmtpMessage)server.ReceivedEmail[0];
        Assert.Equal("[email protected]", mail.Headers["From"]);
        Assert.Equal("[email protected]", mail.Headers["To"]);
        Assert.Equal("subject", mail.Headers["Subject"]);
        Assert.Equal("body", mail.MessageParts[0].BodyData);
        server.Stop();
    }
}

运行结果：