DbContext Mocking ChangeTracker with xUnit - Entity Framework

Question

I am currently trying to track changes done to the entities. The application is an ASP.NET MVC app using Entity Framework. Within the repository I use a basic command for saving

DbContext.SaveChangesAsync()

However, before that I would like to check what have changed in the entity and thus I use

DbContext.ChangeTracker.Entries<TEntity>();

All works fine when I am running the solution, but starting up the xUnit unit tests returns an error

System.InvalidOperationException : No connection string named "XXXX" could be found in the application config file

It seems like the mocking that I do doesn't mock the ChangeTracker - how can I achieve it so that I can mock the change tracker? Is there maybe other option how to prevent such a problem? How do you normally mock the DbContext so that it covers the change tracker as well?

Example of the code:

        public virtual async Task UpdateAsync(params TEntity[] items)
    {

        foreach (var item in items.Where(i => i != null).ToList())
        {
            if (item.Id == 0)
            {
                throw new CustomException(CustomExceptionReason.CannotUpdateNotCreated, item.Id.ToString());
            }

            DbContext.ChangeTracker.DetectChanges();
            var otherCHanges = DbContext.ChangeTracker.Entries<TEntity>();

            UpdateModifiedDate(item);

        }

        await this.DbContext.SaveChangesAsync();


        foreach (var item in items)
        {
            CacheRemove(item);
        }
    }

Example of mocking:

var users = new[] { new User {Id = 1, UserName = "TestUserName", FirstName = "Test", LastName = "User"} }; 

var dbContextMock = new DbContextMock<MyEntities>();
dbContextMock.CreateDbSetMock(x => x.Users, (e, c) => e.Id, users);

Thank you!