Moq testing Entity Framework

Question

I am newbie to both Entity Framework and Moq testing .

Below is my EF code :

public class Repository<TEntity> : IRepository<TEntity> where TEntity : class
{

    protected readonly DbContext Context;
    public Repository(DbContext context)
    {
        Context = context;
    }

    public TEntity Get(int id)
    {
      
        return Context.Set<TEntity>().Find(id);
    }

    public IEnumerable<TEntity> GetAll()
    {
       
        return Context.Set<TEntity>().ToList();
    }

    public void Add(TEntity entity)
    {
        Context.Set<TEntity>().Add(entity);
    }

    public void Remove(TEntity entity)
    {
        Context.Set<TEntity>().Remove(entity);
    }

}


public interface IRepository<TEntity> where TEntity : class
{

    TEntity Get(int id);
    IEnumerable<TEntity> GetAll();


    void Add(TEntity entity);

    void Remove(TEntity entity);

}


public interface IUnitOfWork : IDisposable
{

    int Complete();
}


public class UnitOfWork : IUnitOfWork
{


    private readonly EF_SalesOrdersDBContext _context;

    public CustomersRepository customersRepository { get; set; }

    public UnitOfWork(EF_SalesOrdersDBContext context)
    {
        _context = context;
        customersRepository = new CustomersRepository(_context);
    }



    public int Complete()
    {
        return _context.SaveChanges();
    }

    public void Dispose()
    {
        _context.Dispose();
    }
}

public class CustomersRepository : Repository<Customer>
{
    public CustomersRepository(EF_SalesOrdersDBContext context)
        :base(context)
    {
            
    }



}

Code below in program.cs which works.

   UnitOfWork unitOfWork = new UnitOfWork(new EF_SalesOrdersDBContext());
        unitOfWork.customersRepository.Add(new Customer { CompanyName = "test2", FirstName = "John", LastName = "Barnes", AddressLine1 = "11 lfc", City = "Liverpool", County = "LFC", Phone = "444" });         
        unitOfWork.Complete();

I would like test using Moq .

This is what I have tried:

 [TestClass]
public class UnitTest1
{
    [TestMethod]
    public void TestMethod1()
    {
  
        var mockSet = new Mock<DbSet<Customer>>();

        var mockContext = new Mock<EF_SalesOrdersDBContext>();
        mockContext.Setup(m => m.Customers).Returns(mockSet.Object);


        var service = new CustomersRepository(mockContext.Object);

   

        service.Add(new Customer { CompanyName = "test2", FirstName = "John", LastName = "Barnes", AddressLine1 = "11 lfc", City = "Liverpool", County = "LFC", Phone = "444" });

        mockSet.Verify(m => m.Add(It.IsAny<Customer>()), Times.Once());
        mockContext.Verify(m => m.SaveChanges(), Times.Once());


    }

}

I get the error:

Message: Test method UnitTestProject1.UnitTest1.TestMethod1 threw exception: System.NullReferenceException: Object reference not set to an instance of an object. Stack Trace: Repository`1.Add(TEntity entity) line 34 UnitTest1.TestMethod1() line 26

Answer 1

Mocking db context is a bad idea - you can simply use an in memory context and avoid mocking everything. It will work just like the real database.

See these suggestions from Microsoft: https://docs.microsoft.com/en-us/ef/core/testing/

This question has some answers that show how to make the in memory context: Unit testing with EF Core and in memory database

Answer 2

A key reason for implementing a repository pattern with Entity Framework is to enable unit testing. The Repository becomes the abstraction point for the unit tests. Basically think of it this way:

• You trust that EF is written and tested correctly to guarantee you'll get what you're supposed to get.
• The repository's purpose is solely to serve as a relay, containing no high-level business logic.
• Any low-level rules that a repository may enforce that are dependent on Data State will be covered by integration tests. These tests would be run using either a known-state snapshot database or in-memory database.

So where your main business logic should be residing in your Services / Controllers, that is where your unit tests would be targeting. The Mocks are made for your Repositories, not EF DbContexts/DbSets.

So for example, given your structure I would have a Mock of the UnitOfWork which asserts whether any Complete() call is made (or not), then mock out the Repository for expected methods to return a known state.