add test suite

yes, there is. Mark location with `N_` and then translate usage. see: 
* https://github.com/yast/yast-registration/blob/3c603c9b9f8ece2ed7a921ac38c5de66599b7b5d/src/clients/inst_scc.rb#L52 (marking)
* https://github.com/yast/yast-registration/blob/3c603c9b9f8ece2ed7a921ac38c5de66599b7b5d/src/clients/inst_scc.rb#L146 (usage of translation of constant( or any string) )
* https://github.com/yast/yast-registration/blob/3c603c9b9f8ece2ed7a921ac38c5de66599b7b5d/src/clients/inst_scc.rb#L46 ( required to use N_ as class method )