/**
  * Adds new group to payment methods for this country.
  * If some other group was registered earlier with same key, overwrites it.
  * Returns given group
  *
  * @param WebToPay_PaymentMethodGroup $group
  *
  * @return WebToPay_PaymentMethodGroup
  */
 public function addGroup(WebToPay_PaymentMethodGroup $group)
 {
     return $this->groups[$group->getKey()] = $group;
 }