public decimal CalculateOrderDiscount(IEnumerable<Product> products, Customer customer)
 {
     // do work
     throw new NotImplementedException();
 }
 public void Register(Customer customer)
 {
     // do work
 }
 public void ForgotPassword(Customer customer)
 {
     // do work
 }
 public IEnumerable<string> GatherOrderErrors(IEnumerable<Product> products, Customer customer)
 {
     // do work
     throw new NotImplementedException();
 }
 public bool CustomerIsValid(Customer customer, Order order)
 {
     // do work
     throw new NotImplementedException();
 }