EF Code First and WPF with the Chinook database. Part 1c – the unit tests

In the final part of the server side code (we have already written a Code First provider and data provider), I am going to implement some unit tests for the two methods I currently have on the data provider.

My unit tests will need to have no access to the database as that would break the encapsulation of the test so we need to mock out the raw data access layer while still providing the functionality that we would expect from the Entity Framework context.

To do this, we need to make several changes to the current project to allow us to inject a mocked up context into the data provider.

The first thing we need to do is to abstract the context used by the data provider out into an interface, being as we currently have a small set of classes then the interface is simply:

public interface IContext
{
    IDbSet<Artist> Artist { get; set; }

    IDbSet<Album> Album { get; set; }

    IDbSet<Track> Track { get; set; }
}

Notice the IDbSet<T> – this is to allow us to mock up the DbSets using the same interface.

Next up, we need to edit our Chinook class so that it uses this new interface (note, again, the IDbSet<T>s).

public class Chinook : DbContext, IContext
{
    protected override void OnModelCreating
	(System.Data.Entity.ModelConfiguration.ModelBuilder modelBuilder)
    {
        modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
    }

    public IDbSet<Artist> Artist { get; set; }

    public IDbSet<Album> Album { get; set; }

    public IDbSet<Track> Track { get; set; }
}

Now that we have this, we can use the interface in the data provider and set it to a Chinook instance by default (for the time being).

private IContext db = new Chinook();

Right now, we have a good basis to start working on the test so add a new test project to the solution and create a new class called MockDbSet. This allows us to simulate the actions of a real DbSet in the database for a given set of objects. Huge thanks to Julie Lerman for showing the starting point for this work with her series on EF4 repositories (A great read!).

The MockDbSet implements the IDbSet<T> Interface supplied by the Entity Framework and allows us to replicate the functionality as follows (note that I have not implemented the create or find methods as I don’t need them right now.)

public class MockDbSet<T> : IDbSet<T> where T : class
{
    readonly IList<T> _container = new List<T>();

    public T Add(T entity)
    {
        _container.Add(entity);
        return entity;
    }

    public T Attach(T entity)
    {
        _container.Add(entity);
        return entity;
    }

    public TDerivedEntity Create<TDerivedEntity>() where TDerivedEntity : class, T
    {
        throw new NotImplementedException();
    }

    public T Create()
    {
        throw new NotImplementedException();
    }

    public T Find(params object[] keyValues)
    {
        throw new NotImplementedException();
    }

    public System.Collections.ObjectModel.ObservableCollection<T> Local
    {
        get
        {
            return new ObservableCollection<T>(_container);
        }
    }

    public T Remove(T entity)
    {
        _container.Remove(entity);
        return entity;
    }

    public IEnumerator<T> GetEnumerator()
    {
        return _container.GetEnumerator();
    }

    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
    {
        return _container.GetEnumerator();
    }

    public Type ElementType
    {
        get
        {
            return typeof(T);
        }
    }

    public System.Linq.Expressions.Expression Expression
    {
        get
        {
            return _container.AsQueryable<T>().Expression;
        }
    }

    public IQueryProvider Provider
    {
        get
        {
            return _container.AsQueryable<T>().Provider;
        }
    }
 }

This is a simple implementation that stores the set in a local List.

Now that we have a mock set, we can mock up the context which is something that implements IContext and allows us to access the DbSets we want to work with outside of a database environment. I have added some methods to add test data into the sets as well.

class MockContext : IContext
{
    private IDbSet<Artist> artist;
    private IDbSet<Album> album;
    private IDbSet<Track> track;

    public IDbSet<Artist> Artist
    {
        get
        {
            this.CreateArtists();
            return this.artist;
        }

        set
        {
            throw new NotImplementedException();
        }
    }

    public IDbSet<Album> Album
    {
        get
        {
            this.CreateAlbums();
            return this.album;
        }

        set
        {
            throw new NotImplementedException();
        }
    }

    public IDbSet<Track> Track
    {
        get
        {
            this.CreateTracks();
            return this.track;
        }

        set
        {
            throw new NotImplementedException();
        }
    }

    private void CreateArtists()
    {
        if (artist == null)
        {
            artist = new MockDbSet<Artist>();
            artist.Add(new Artist { ArtistId = 1, Name = "Test Artist 1" });
            artist.Add(new Artist { ArtistId = 2, Name = "Test Artist 2" });
            artist.Add(new Artist { ArtistId = 3, Name = "Test Artist 3" });
        }
    }

    private void CreateAlbums()
    {
        if (album == null)
        {
            album = new MockDbSet<Album>();
            album.Add(new Album { AlbumId = 1, Title = "Test Album 1", ArtistId = 1 });
            album.Add(new Album { AlbumId = 2, Title = "Test Album 2", ArtistId = 2 });
            album.Add(new Album { AlbumId = 3, Title = "Test Album 3", ArtistId = 3 });
            album.Add(new Album { AlbumId = 4, Title = "Test Album 4", ArtistId = 3 });
        }
    }

    private void CreateTracks()
    {
        if (track == null)
        {
            track = new MockDbSet<Track>();
            track.Add(new Track { TrackId = 1, Name = "Test Track 1", AlbumId = 1 });
            track.Add(new Track { TrackId = 2, Name = "Test Track 2", AlbumId = 1 });
            track.Add(new Track { TrackId = 3, Name = "Test Track 3", AlbumId = 1 });
            track.Add(new Track { TrackId = 4, Name = "Test Track 4", AlbumId = 2 });
            track.Add(new Track { TrackId = 5, Name = "Test Track 5", AlbumId = 2 });
            track.Add(new Track { TrackId = 6, Name = "Test Track 6", AlbumId = 2 });
            track.Add(new Track { TrackId = 7, Name = "Test Track 7", AlbumId = 3 });
            track.Add(new Track { TrackId = 8, Name = "Test Track 8", AlbumId = 3 });
            track.Add(new Track { TrackId = 9, Name = "Test Track 9", AlbumId = 4 });
            track.Add(new Track { TrackId = 10, Name = "Test Track 10", AlbumId = 4 });
        }
    }
}

Now that we have a context and sets mocked up, we can almost write our tests but at the moment we have no way of getting the new mock context into the data provider. This is where we can use an often overlooked assembly attribute, InternalsVisibleTo, which allows the given project access to internal members of the project. So all we need to do is apply the following to the AssemblyInfo.cs class of the model project.

[assembly: InternalsVisibleTo("MusicApp.Model.Tests")]

and change the context member in the data provider (db) from private to internal and we can access it from the our test project.

I have two tests – one for each method in the data provider and have implemented them as follows:

public class EFCodeFirstDataProviderTest
{
    [TestMethod()]
    public void GetArtistsTest()
    {
        EFCodeFirstDataProvider target = new EFCodeFirstDataProvider() 
					{ db = new MockContext() };

        List<Artist> expected = new List<Artist>();
        expected.Add(new Artist { ArtistId = 1, Name = "Test Artist 1" });
        expected.Add(new Artist { ArtistId = 2, Name = "Test Artist 2" });
        expected.Add(new Artist { ArtistId = 3, Name = "Test Artist 3" });

        List<Artist> actual = target.GetArtists();
        CollectionAssert.AreEquivalent(expected, actual);
    }

    [TestMethod()]
    public void SearchArtistsTest()
    {
        EFCodeFirstDataProvider target = new EFCodeFirstDataProvider() 
					{ db = new MockContext() };

        string searchTerm = "Artist 1";
        List<Artist> expected = new List<Artist>();
        expected.Add(new Artist { ArtistId = 1, Name = "Test Artist 1" });

        List<Artist> actual = target.SearchArtists(searchTerm);

        CollectionAssert.AreEquivalent(expected, actual);
    }
}

As you can see, they are simple tests to determine that the methods return the objects that I wanted. As they stand, these methods will fail as the CollectionAssert.AreEquivalent method checks for equality and we have no override for equality (or hash code) in our Artist class so we just need to add them in:

public override int GetHashCode()
{
    return ArtistId;
}

public override bool Equals(object obj)
{
    return ArtistId == (obj as Artist).ArtistId;
}

and the tests will now pass.

In the next post, I will create a simple WPF front-end to display the information and then I will build the interface from that point on.