Converting an IQueryable<T> to a DbSet<T>

Question

I'm not sure that this is possible, but I'm trying to unit test a repository that uses a DbSet. I thought the easiest solution would just be to make an Enumerable, and replace the DbSet with that, this is my attempt.

I'm using C#, EntityFramework, XUnit, and Moq

[Fact]
public void SomeTest() 
{
    //arrange
    var mockContext = new Mock<MyDbContext>();
    var mockData = new List<Person>
        {
            new Person { Name = "Jim", Age = 47 }
        };
    mockContext.Setup(db => db.Persons).Returns((DbSet<Person>)mockData.AsQueryable());

    var repo = PersonRepository(mockContext.Object); 

    //act
    var result = repo.GetByFirstName("Jim");

    //assert
    //do some assertion
}

The error that gets thrown is it can't convert type EnumerableQuery to a DbSet on the mockContext.Returns statement.

Here is something similar to what the interfaces look like.

PersonRepository.cs

public class PersonRepository: EFRepository<Person>, IPersonRepository
{
    public PersonRepository(DbContext dbContext) : base(dbContext)
    {
    }

    public IQueryable<Link> GetByFirstName(string name)
    {
        return DbSet.Where(p => p.FirstName == name);
    }
}

IPersonRepository.cs

public interface IPersonRepository: IRepository<Person>
{
    IQueryable<Person> GetByFirstName(string name);
}

IRepository.cs

public interface IRepository<T> where T : class 
{
    IQueryable<T> GetAll();
    T GetById(int id);
    void Add(T entity);
    void Delete(T entity);
    void Delete(int id);
    void Update(T entity);
}

EFRepository.cs

public class EFRepository<T> : IRepository<T> where T : class
{
    protected DbContext DbContext { get; set; }
    public IDbSet<T> DbSet { get; set; }

    public EFRepository(DbContext dbContext)
    {
        if (dbContext == null)
            throw new ArgumentNullException("dbContext");

        DbContext = dbContext;
        DbSet = DbContext.Set<T>();
    }
    ...
}

Answer 1

What you can do is to move the Linq expression from your repository into the business logic and mock the repository instead.

public interface IPersonRepository : IRepository<Person>
{
    IQueryable<Person> GetAll { get; }
}

public class PersonRepository : EFRepository<Person>, IPersonRepository
{
    // ...

    public IQueryable<Person> GetAll
    {
        get { return DbSet; }
    }
}

public class SomeBusinessLogicClass
{
    private readonly IPersonRepository _people;

    public SomeBusinessLogicClass(IPersonRepository people)
    {
        _people = people;
    }

    public IEnumerable<Person> GetByFirstName(string name)
    {
        return _people.GetAll.Where(p => p.FirstName == name);
    }
}

Now rewrite your test to validate the business logic.

[Fact]
public void SomeTest() 
{
    //arrange
    var mockRepository = new Mock<IPersonRepository>();
    var mockData = new List<Person>
        {
            new Person { Name = "Jim", Age = 47 }
        };
    mockRepository.Setup(x => x.GetAll).Returns(mockData);

    var bl = new SomeBusinessLogicClass(mockRepository.Object); 

    //act
    var result = bl.GetByFirstName("Jim");

    //assert
    //do some assertion
}