Test Entity Framework Find Method

Question

I'm trying to test the that the GetSystem(int id) method in SystemService.cs returns the correct value, but can't seem to figure out how to get everything to play well together. It seems that no matter what I do, GetSystem() always returns null. This is using Entity Framework 6. If I change the body of GetSystem to read _context.Systems.SingleOrDefault(s => s.Id = id) , then everything works properly, but I'd really like to use Find() .

What is the proper way to test this? I'm using xUnit and Moq in this example. SystemServiceTests.cs shows the code that I'm currently using that isn't working.

SystemService.cs

namespace MyProject.Services
{
  public class SystemService
  {
    private readonly MyContext _context;

    public SystemService(MyContext context)
    {
      _context = context;
    }

    public Models.System GetSystem(int id)
    {
      return _context.Systems.Find(id);
    }
  }
}

SystemServiceTests.cs

namespace MyProject.Tests.Unit
{
  public class SystemServiceTests
  {
    [Fact]
    public void GetSystemReturnsFromContext()
    {
      var data = new List<Models.System> {
        new Models.System { Id = 1, Name = "test 1" },
        new Models.System { Id = 2, Name = "test 2" }
      }.AsQueryable();

      var mockContext = new Mock<MyContext>();

      var mockSet = new Mock<MockableDbSetWithIQueryable<Models.System>>();
      mockContext.Setup(c => c.Systems).Returns(mockSet.Object);

      mockSet.Setup(m => m.Provider).Returns(data.Provider);
      mockSet.Setup(m => m.Expression).Returns(data.Expression);
      mockSet.Setup(m => m.ElementType).Returns(data.ElementType);
      mockSet.Setup(m => m.GetEnumerator()).Returns(data.GetEnumerator());

      var service = new SystemService(mockContext.Object);
      var system = service.GetSystem(1);

      Assert.NotNull(system); // This is always null
    }
  }
}

MyContext.cs

namespace MyProject.Models
{
  public class MyContext : DbContext
  {
    public MyContext()
      : base("DefaultConnection")
    {
    }

    public virtual DbSet<Models.System> Systems { get; set; }
  }
}

System.cs

namespace MyProject.Models
{
  public class System
  {
    public int Id { get; set; }
    public string Name { get; set; }
  }
}

MockableDbSetWithIQueryable.cs

namespace MyProject.Tests.Helpers
{
  public abstract class MockableDbSetWithIQueryable<T> : DbSet<T>, IQueryable
    where T : class
  {
    public abstract IEnumerator<T> GetEnumerator();
    public abstract Expression Expression { get; }
    public abstract Type ElementType { get; }
    public abstract IQueryProvider Provider { get; }
  }
}

PS. Some of the code for this, specifically MockableDbSetWithIQueryable was found at http://msdn.microsoft.com/en-US/data/dn314429

Answer 1

I was able to find the recommended way to test everything using Entity Framework 6. The resource for this recommendation is available at http://msdn.microsoft.com/en-US/data/dn314431 .

In a nutshell, test classes need to be created for each bit that needs to be tested. What I ended up doing is the following:

TestDbSet.cs

public class TestDbSet<TEntity> : DbSet<TEntity>, IQueryable, IEnumerable<TEntity>
    where TEntity : class
{
    ObservableCollection<TEntity> _data;
    IQueryable _query;

    public TestDbSet()
    {
        _data = new ObservableCollection<TEntity>();
        _query = _data.AsQueryable();
    }

    public override TEntity Add(TEntity item)
    {
        _data.Add(item);
        return item;
    }

    public override TEntity Remove(TEntity item)
    {
        _data.Remove(item);
        return item;
    }

    public override TEntity Attach(TEntity item)
    {
        _data.Add(item);
        return item;
    }

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

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

    public override ObservableCollection<TEntity> Local
    {
        get
        {
            return _data;
        }
    }

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

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

    IQueryProvider IQueryable.Provider
    {
        get { return _query.Provider; }
    }

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

    IEnumerator<TEntity> IEnumerable<TEntity>.GetEnumerator()
    {
        return _data.GetEnumerator();
    }
}

TestSystemDbSet.cs

class TestSystemDbSet : TestDbSet<Models.System>
{
    public override Models.System Find(params object[] keyValues)
    {
        var id = (int)keyValues.Single();
        return this.SingleOrDefault(s => s.Id == id);
    }
}

TestContext.cs

public class TestContext: IContext
{
    public TestContext()
    {
        this.Systems = new TestSystemDbSet();
    }

    public DbSet<Models.System> Systems { get; set; }

    public int SaveChangesCount { get; private set; }
    public int SaveChanges()
    {
        this.SaveChangesCount++;
        return 1;
    }
}

SystemServiceTests.cs

public class SystemServiceTests
{
    [Fact]
    public void GetSystemReturnsFromContext()
    {
        var context = new TestContext();
        context.Systems.Add(new Models.System { Id = 1, Name = "System 1" });
        context.Systems.Add(new Models.System { Id = 2, Name = "System 2" });
        context.Systems.Add(new Models.System { Id = 3, Name = "System 3" });

        var service = new SystemService(context);
        var system = service.GetSystem(2);

        Assert.NotNull(system);
        Assert.Equal(2, system.Id);
        Assert.Equal("System 2", system.Name);
    }
}

SystemService.cs

public class SystemService : ISystemService
{
    private readonly IContext _context;

    public SystemService(IContext context)
    {
        _context = context;
    }

    public Models.System AddSystem(Models.System system)
    {
        var s = _context.Systems.Add(system);
        _context.SaveChanges();

        return s;
    }

    public Models.System GetSystem(int id)
    {
        return _context.Systems.Find(id);
    }
}

ISystemService.cs

public interface ISystemService
{
    Models.System AddSystem(Models.System system);
    Models.System GetSystem(int id);
}

Answer 2

.Find() is returning null because that is the default value for System . The collection does not contain an item with id id .

.Find() is a method of List .

I suggest you use LINQ's FirstOrDefault()

The reason being, you can use lazy loading by returning an IQueryable