Mock FirstOrDefault returns NullReferenceException

Question

I would like to understand why my mock dbset is throwing a NullReferenceException when I call dbContext.Object.Locations.FirstOrDefault(x => x.Id == id);

I have setup my mock dbset as detailed below:

public Mock<DbSet<T>> GetMockDbSet<T>(string path) where T : class
{
     var data = GetObjectList<T>(path).AsQueryable();

     var mockSet = new Mock<DbSet<T>>();
     mockSet.As<IQueryable<T>>().Setup(m => m.Provider).Returns(data.Provider);
     mockSet.As<IQueryable<T>>().Setup(m => m.Expression).Returns(data.Expression);
     mockSet.As<IQueryable<T>>().Setup(m => m.ElementType).Returns(data.ElementType);
     mockSet.As<IQueryable<T>>().Setup(m => m.GetEnumerator()).Returns(()=>data.GetEnumerator());

     return mockSet;
}

private Mock<DbContext> LoadMockDataBase(ref Dictionary<string, object> mockDictionary)
{
     var mockSetLocations = GetMockDbSet<Repository.Location>(@"Files/ObjectJson/Locations.json");
     dbContext.Setup(l => l.Locations).Returns(mockSetLocations.Object);
     dbContext.Setup(x => x.Locations.AsNoTracking()).Returns(mockSetLocations.Object);
     return dbContext;
}

I understand that if I remove AsNoTracking() this fixes the issue however I do not want to limit the application on not using AsNoTracking simply for passing tests when the logic is correct.

Answer 1

This solved the issue. For anyone having issues in the future where AsNoTracking() or FirstOrDefault() are returning a NUllException.

   public Mock<DbSet<T>> GetMockDbSet<T>(string path) where T : class
        {
            var data = GetObjectList<T>(path).AsQueryable();

            var mockSet = new Mock<DbSet<T>>();
            mockSet.As<IQueryable<T>>().Setup(m => m.Provider).Returns(data.Provider);
            mockSet.As<IQueryable<T>>().Setup(m => m.Expression).Returns(data.Expression);
            mockSet.As<IQueryable<T>>().Setup(m => m.ElementType).Returns(data.ElementType);
            mockSet.As<IQueryable<T>>().Setup(m => m.GetEnumerator()).Returns(()=>data.GetEnumerator());

            mockSet.Setup(x => x.AsNoTracking()).Returns(mockSet.Object);

            return mockSet;
        }