[C#][Moq][EF 6] Fake Add method

I'm struggling with faking my DbContext classes. Let's say I have my DbContext with entity Cars. I did manage to fake a list of Cars, but now I don't know how to fake adding (so adding would add a new Car to my fake list).

I have my list of Cars (this class is generic, but to give an easy example I've changed it to Cars):

private List<Cars> Data;

And property which returns Moq object:

    public Mock<DbSet<Cars>> MockSet
    {
        get
        {
            var mock = new Mock<DbSet<Cars>>();
            mock.As<IQueryable<Cars>>().Setup(m => m.Provider).Returns(Data.Provider);
            mock.As<IQueryable<Cars>>().Setup(m => m.Expression).Returns(Data.Expression);
            mock.As<IQueryable<Cars>>().Setup(m => m.ElementType).Returns(Data.ElementType);
            mock.As<IQueryable<Cars>>().Setup(m => m.GetEnumerator()).Returns(Data.GetEnumerator());

            //To fake Include:
            mock.Setup(m => m.Include(It.IsAny<String>())).Returns(mock.Object);
            return mock;
        }
    }

If I have this object, I can fake my entity:

        Mock<DBContext>  dbMoq = new Mock<DbContext>();
        dbMoq.Setup(x => x.Cars).Returns(carsMoq.MockSet.Object);

Now I'm able to run my test without any problem, but if within my test method someone will add a new Car, I won't be able to check it:

 this.dbContext.Cars.Add(car); 

I did try to mock Add method and add new entity to my fake list:

        dbMoq.Setup(x => x.Cars.Add(It.IsAny<Cars>())).Callback<Cars>((c) => this.CarsList.Add(c));

But it seems to do nothing. Any clue for that ? Is this approach a good one ?