UrlShortener.cs

using Microsoft.VisualStudio.TestTools.UnitTesting;
using Moq;

namespace UrlShortener.Tests
{
    [TestClass]
    public class UrlShortener_Tests
    {
        private Shortener _service;
        private Mock<IShortenerEngine> _engine;
        private Mock<IRepository> _repMock;

        [TestInitialize]
        public void TestIntialize()
        {
            _engine = new Mock<IShortenerEngine>();
            _repMock = new Mock<IRepository>();
            _service = new Shortener(_engine.Object, _repMock.Object);
        }

        [TestMethod]
        public void GetShortUrl_should_pass_url_to_shortenerEngine()
        {
            //Arrange
            string longUrl = "http://super.long.url.com/blablabla";

            // Act
            _service.GetShortUrl(longUrl);

            // Assert
            _engine.Verify(e => e.GetShortUrl(longUrl), Times.Once);
        }

        [TestMethod]
        public void GetShortUrl_should_save_short_url_to_repository()
        {
            // Arrange
            string originalUrl = "http://super.long.url.com/blablabla";
            string shortUrl = "http://s.com/1";
            _engine.Setup(s => s.GetShortUrl(originalUrl))
                .Returns(shortUrl);

            // Act
            _service.GetShortUrl(originalUrl);

            // Assert
            _repMock.Verify(r => r.Save(shortUrl, originalUrl));
        }
    }

    public interface IRepository
    {
        void Save(string shortUrl, string originalUrl);
    }

    public class Shortener : IShortener
    {
        private readonly IShortenerEngine _shortenerEngine;
        private readonly IRepository _repository;

        public Shortener(IShortenerEngine shortenerEngine, IRepository repository)
        {
            _shortenerEngine = shortenerEngine;
            _repository = repository;
        }

        public string GetShortUrl(string url)
        {
           string shortUrl =  _shortenerEngine.GetShortUrl(url);
            _repository.Save(shortUrl, url);
            return shortUrl;
        }
    }

    public interface IShortener
    {
        string GetShortUrl(string url);
    }

    public interface IShortenerEngine
    {
        string GetShortUrl(string url);
    }
}