add test suite

OK, so it is mixture of structure which hold dialog values and logic ( like read/write, presets ). If it was really structure, then preset will be instance of such structure and read/write will read/write such structure. Ruby have for structures quite nice classes - http://www.ruby-doc.org/core-2.1.2/Struct.html and http://www.ruby-doc.org/stdlib-2.0/libdoc/ostruct/rdoc/OpenStruct.html

example of usage is e.g. in registration - https://github.com/yast/yast-registration/blob/3c603c9b9f8ece2ed7a921ac38c5de66599b7b5d/src/lib/registration/storage.rb#L53