private static void RentalAdded()
{
RentalManager rentalManager = new RentalManager(new EfRentalDal());
var result = rentalManager.Added(new Rental {
RentalId = 4, CarId = 1, CustomerId = 4, RentDate = new DateTime(2020, 12, 03), ReturnDate = null
});
Console.WriteLine(result.Message);
}