Unit testing with EF4 "Code First" and Repository

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I am attempting to get a handle on Unit testing a very simple ASP.NET MVC test app I've built using the Code First approach in the latest EF4 CTP. I'm not very experience with Unit testing / mocking etc.

This is my Repository class:

public class WeightTrackerRepository
{
    public WeightTrackerRepository()
    {
        _context = new WeightTrackerContext();
    }

    public WeightTrackerRepository(IWeightTrackerContext context)
    {
        _context = context;
    }

    IWeightTrackerContext _context;

    public List<WeightEntry> GetAllWeightEntries()
    {
        return _context.WeightEntries.ToList();
    }

    public WeightEntry AddWeightEntry(WeightEntry entry)
    {
        _context.WeightEntries.Add(entry);
        _context.SaveChanges();
        return entry;
    }
}

This is IWeightTrackerContext

public interface IWeightTrackerContext
{
    DbSet<WeightEntry> WeightEntries { get; set; }
    int SaveChanges();
}

...and its implementation, WeightTrackerContext

public class WeightTrackerContext : DbContext, IWeightTrackerContext
{
    public DbSet<WeightEntry> WeightEntries { get; set; }
}

In my test, I have the following:

[TestMethod]
public void Get_All_Weight_Entries_Returns_All_Weight_Entries()
{
    // Arrange
    WeightTrackerRepository repos = new WeightTrackerRepository(new MockWeightTrackerContext());

    // Act
    List<WeightEntry> entries = repos.GetAllWeightEntries();

    // Assert
    Assert.AreEqual(5, entries.Count);
}

And my MockWeightTrackerContext:

class MockWeightTrackerContext : IWeightTrackerContext
{
    public MockWeightTrackerContext()
    {
        WeightEntries = new DbSet<WeightEntry>();
        WeightEntries.Add(new WeightEntry() { Date = DateTime.Parse("01/06/2010"), Id = 1, WeightInGrams = 11200 });
        WeightEntries.Add(new WeightEntry() { Date = DateTime.Parse("08/06/2010"), Id = 2, WeightInGrams = 11150 });
        WeightEntries.Add(new WeightEntry() { Date = DateTime.Parse("15/06/2010"), Id = 3, WeightInGrams = 11120 });
        WeightEntries.Add(new WeightEntry() { Date = DateTime.Parse("22/06/2010"), Id = 4, WeightInGrams = 11100 });
        WeightEntries.Add(new WeightEntry() { Date = DateTime.Parse("29/06/2010"), Id = 5, WeightInGrams = 11080 });
    }

    public DbSet<WeightEntry> WeightEntries { get;set; }

    public int SaveChanges()
    {
        throw new NotImplementedException();
    }
}

My problem occurs when I'm trying to build up some test data as I can't create a DbSet<> as it has no constructor. I get the feeling I'm barking up the wrong tree with my whole approach trying to mock my context. Any advice would be most welcome to this complete unit testing newbie.

entity-framework-4 mocking unit-testing asp.net-mvc c#
3 Answers

Building on what Daz said, (and as I mentioned in his comments), you are going to need to make a 'fake' implementation of IDbSet. An example for CTP 4 can be found here but to get it to work you'll have to customize your Find method and add return values for a couple of the previously void-ed methods, like Add.

The following is my own crafted example for CTP 5:

public class InMemoryDbSet<T> : IDbSet<T> where T : class
{
    readonly HashSet<T> _data;
    readonly IQueryable _query;

    public InMemoryDbSet()
    {
        _data = new HashSet<T>();
        _query = _data.AsQueryable();
    }

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

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

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

    public T Create()
    {
        return Activator.CreateInstance<T>();
    }

    public virtual T Find(params object[] keyValues)
    {
        throw new NotImplementedException("Derive from FakeDbSet and override Find");
    }

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

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

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

    IEnumerator IEnumerable.GetEnumerator()
    {
        return _data.GetEnumerator();
    }

    public Type ElementType
    {
        get { return _query.ElementType; }
    }

    public Expression Expression
    {
        get { return _query.Expression; }
    }

    public IQueryProvider Provider
    {
        get { return _query.Provider; }
    }
}
user_603850
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