See http://debbugs.gnu.org/cgi/bugreport.cgi?bug=37318.
* gnu/services/networking.scm (openntpd-configuration->string): New procedure,
extracted from top of the `openntpd-shepherd-service' to make it testable.
(openntpd-shepherd-service): Adapt following the move of the code to the above
procedure.
* tests/networking.scm: Add a test for the `openntpd-configuration->string'
procedure.