Hi Vlumansi,
The information you require is in ICAO Doc 8071 "Manual of Testing of Radio Navigational Aids Vol 1" This places responsibility on the State to establish the status of the Nav Aid facility. The State can authorise/approve an organisation to carry out a flight inspection and the persons involved should be formally certified by the State as part of the approval.
UK CAA CAP 670 contains requirements for the Approval of Flight Inspection Organisations.
https://publicapps.caa.co.uk/docs/33...May%202014.pdf