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exercise3.md

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Importance of testing your projects

Learnings

  1. Create mock implementations
  2. Unit-Tests
  3. Build Automation with Unit-Tests

Create an interface for feed retrieval

  1. Discuss the need of an interface
  2. Create a folder Manager
  3. Add a new interface called IFeedManager.cs
    public interface IFeedManager<T>
{
    Task<IEnumerable<T>> LoadItemsAsync(string search = null);
}

Create an implementation for Twitter

  1. Add a new class called TwitterManager.cs
  2. You can copy most of the code from the existing TwitterViewModel.cs 
    public class TwitterManager : IFeedManager<Tweet>
{
    private IAuthorizer auth;

    public TwitterManager(string consumerKey, string consumerSecret)
    {
        this.auth = new ApplicationOnlyAuthorizer()
        {
            CredentialStore = new InMemoryCredentialStore
            {
                ConsumerKey = "ZTmEODUCChOhLXO4lnUCEbH2I",
                ConsumerSecret = "Y8z2Wouc5ckFb1a0wjUDT9KAI6DUat5tFNdmIkPLl8T4Nyaa2J",
            },
        };
    }

    public async Task<IEnumerable<Tweet>> LoadItemsAsync(string search = null)
    {

        await auth.AuthorizeAsync();

        var twitterContext = new TwitterContext(auth);

        var query = from tweet in twitterContext.Status
                    where tweet.Type == StatusType.User &&
                            tweet.ScreenName == "shanselman" &&
                            tweet.Count == 100 &&
                            tweet.IncludeRetweets == true &&
                            tweet.ExcludeReplies == true &&
                            (string.IsNullOrWhiteSpace(search) || tweet.Text.Contains(search))
                    select tweet;

        var queryResponse = await query.ToListAsync();

        return (from tweet in queryResponse
                select new Tweet
                {
                    StatusID = tweet.StatusID,
                    ScreenName = tweet.User.ScreenNameResponse,
                    Text = tweet.Text,
                    CurrentUserRetweet = tweet.CurrentUserRetweet,
                    CreatedAt = tweet.CreatedAt,
                    Image = tweet.RetweetedStatus != null && tweet.RetweetedStatus.User != null
                                ? tweet.RetweetedStatus.User.ProfileImageUrl.Replace("http://", "https://")
                                : (tweet.User.ScreenNameResponse == "shanselman"
                                    ? "scott159.png"
                                    : tweet.User.ProfileImageUrl.Replace("http://", "https://"))
                }).ToList();
    }
}

Create a mock implementation

  1. Add a new class called MockTwitterManager.cs 
    public class MockTwitterManager : IFeedManager<Tweet>
{
    public async Task<IEnumerable<Tweet>> LoadItemsAsync(string search = null)
    {
        await Task.Delay(2000);

        var items = new[] {
            new Tweet() { Text = "Tweet1" },
            new Tweet() { Text = "Tweet2" },
            new Tweet() { Text = "Tweet3" },
            new Tweet() { Text = "Tweet4" },
            // required for test
            new Tweet() { Text = "#shanselman" }
        };

        if (!string.IsNullOrWhiteSpace(search))
        {
            items = items.Where(i => i.Text.Contains(search)).ToArray();
        }

        return items;
    }
}

Create a factory (optional)

  1. Discuss the advantages of a factory
  2. Add a new class called ManagerFactory.cs 
    public static class ManagerFactory
{
    public static bool IsMocked { get; set; } = false;

    public static IFeedManager<Tweet> CreateTwitterManager(string consumerKey, string consumerSecret)
    {
        return IsMocked
            ? new MockTwitterManager() as IFeedManager<Tweet>
            : new TwitterManager(consumerKey, consumerSecret);
    }
}

Change the TweetViewModel

  1. Change the affected rows of the TweetViewModel to use the new ManagerFactory

  2. Add a private field

    private IFeedManager<Tweet> twitterManager;

  3. Initialize the field in the constructor

    this.twitterManager = ManagerFactory.CreateTwitterManager(
    "ZTmEODUCChOhLXO4lnUCEbH2I",
    "Y8z2Wouc5ckFb1a0wjUDT9KAI6DUat5tFNdmIkPLl8T4Nyaa2J");

  4. Load the tweets in the ExecuteLoadTweetsCommand method (at the beginning of try/catch)

    var tweets = await this.twitterManager.LoadItemsAsync();

  5. Add a .ToList() in the iOS implementation to solve compiler error

    DependencyService.Get<ITweetStore>().Save(tweets.ToList());

Create a unit test

  1. Add a new Test project called Hanselman.Tests
  2. Create a unit test 
    [TestClass]
public class Tests
{
    [TestInitialize]
    public void Init()
    {
        ManagerFactory.IsMocked = true;
    }

    [TestMethod]
    public async Task LoadTweets()
    {
        var viewModel = new TwitterViewModel();
        var task = viewModel.ExecuteLoadTweetsCommand();

        await CheckIfBusy(task, viewModel);

        Assert.IsTrue(viewModel.Tweets.Any());
    } 

    private async Task CheckIfBusy(Task task, BaseViewModel model)
    {
        Assert.IsTrue(model.IsBusy);
        Assert.IsFalse(model.IsNotBusy);

        await task;

        Assert.IsFalse(model.IsBusy);
        Assert.IsTrue(model.IsNotBusy);
    }
}

Further ideas

You can mock the podcast and blog retrieval as well, see details in the provided sample code. There are also more unit tests available in the solution.

Build Automation with Unit-Tests

The build template, created in Exercise 2 has to be changed.

  1. Got to build definition
  2. click Edit (top-right)
  3. Add new build step
  4. Select Category: Test / Visual Studio Test Build_Test_1
  5. Change the order of the build steps like picture below Build_Test_2
  6. Select Test Assemblies step and change setting Test Assembly to '$(build.binariesdirectory)/$(BuildConfiguration)/test-assembly/Hanselman.Tests.dll' Build_Test_3
  7. Save changes and queue new build

After success the test results appear in the build results overview page. Build_Test_4