using System;

using Moq;

using NUnit.Framework;

​

namespace App;

​

public interface IEmailService {

    void Send(string message);  

}

​

public class Program

{

    public static void Main()

    {

        // Arrange

        // Set everything up.

        var emailService = new Mock<IEmailService>();

        String? passedMessage = null;

        emailService

            .Setup(a => a.Send(It.IsAny<string>()))

            .Callback<string>(msg => {

                passedMessage = msg;

            });

        var emailSender = new EmailSender("Hello", emailService.Object);

        // Act

        // Send the message

        emailSender.SendTo("bill@microsoft.com");

        // Assert

        // Make sure it was sent.

        Assert.AreEqual("Hello", passedMessage);

        Console.WriteLine("Everything is awesome!");

    }

}

​

public class EmailSender {

    private string body;

    private IEmailService emailService;

    public EmailSender(string body, IEmailService emailService) {

        this.body = body;   

        this.emailService = emailService;

    }

    public void SendTo(string emailAddress) {

        emailService.Send(emailAddress);

    }

}

​

public class SmtpEmailService : IEmailService

{

    public void Send(string message)

    {

        // Use SMTPMessage class to send an email with the given message

        // as the body, and forward to an STMP Server.

    }

}

​

public class FakeEmailService : IEmailService

{

    public string? Message;

    public void Send(string message)

    {

        // Save the message in a property so that it can be read back

        Message = message;

    }

}