Mocking EF DbContext with Moq

Question

I'm trying to create a unit test for my service with a mocked DbContext. I created an interface IDbContext with the following functions:

public interface IDbContext : IDisposable {     IDbSet<T> Set<T>() where T : class;     DbEntityEntry<T> Entry<T>(T entity) where T : class;     int SaveChanges(); } 

My real context implements this interface IDbContext and DbContext.

Now I'm trying to mock the IDbSet<T> in the context, so it returns a List<User> instead.

[TestMethod] public void TestGetAllUsers() {     // Arrange     var mock = new Mock<IDbContext>();     mock.Setup(x => x.Set<User>())         .Returns(new List<User>         {             new User { ID = 1 }         });      UserService userService = new UserService(mock.Object);      // Act     var allUsers = userService.GetAllUsers();      // Assert     Assert.AreEqual(1, allUsers.Count()); } 

I always get this error on .Returns:

The best overloaded method match for 'Moq.Language.IReturns<AuthAPI.Repositories.IDbContext,System.Data.Entity.IDbSet<AuthAPI.Models.Entities.User>>.Returns(System.Func<System.Data.Entity.IDbSet<AuthAPI.Models.Entities.User>>)' has some invalid arguments 

Answer 1

I managed to solve it by creating a FakeDbSet<T> class that implements IDbSet<T>

public class FakeDbSet<T> : IDbSet<T> where T : class {     ObservableCollection<T> _data;     IQueryable _query;      public FakeDbSet()     {         _data = new ObservableCollection<T>();         _query = _data.AsQueryable();     }      public virtual T Find(params object[] keyValues)     {         throw new NotImplementedException("Derive from FakeDbSet<T> and override Find");     }      public T Add(T item)     {         _data.Add(item);         return item;     }      public T Remove(T item)     {         _data.Remove(item);         return item;     }      public T Attach(T item)     {         _data.Add(item);         return item;     }      public T Detach(T item)     {         _data.Remove(item);         return item;     }      public T Create()     {         return Activator.CreateInstance<T>();     }      public TDerivedEntity Create<TDerivedEntity>() where TDerivedEntity : class, T     {         return Activator.CreateInstance<TDerivedEntity>();     }      public ObservableCollection<T> Local     {         get { return _data; }     }      Type IQueryable.ElementType     {         get { return _query.ElementType; }     }      System.Linq.Expressions.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<T> IEnumerable<T>.GetEnumerator()     {         return _data.GetEnumerator();     } } 

Now my test looks like this:

[TestMethod] public void TestGetAllUsers() {     //Arrange     var mock = new Mock<IDbContext>();     mock.Setup(x => x.Set<User>())         .Returns(new FakeDbSet<User>         {             new User { ID = 1 }         });      UserService userService = new UserService(mock.Object);      // Act     var allUsers = userService.GetAllUsers();      // Assert     Assert.AreEqual(1, allUsers.Count()); } 

Answer 2

In case anyone is still interested, I was having the same problem and found this article very helpful: Entity Framework Testing with a Mocking Framework (EF6 onwards)

It only applies to Entity Framework 6 or newer, but it covers everything from simple SaveChanges tests to async query testing all using Moq (and a few of manual classes).