Most countries are member of the International Civil Aviation Organization (ICAO) and as such have signed the "Chicago Convention 1944" (111 pages, 2 Mb). Aviation rules and regulations in member countries are based on the recommendations of the ICAO.
The FAA has published an advisory circular for flight testing homebuilt and experimental aircraft.
Amateur-built aircraft and ultralight flight testing handbook.
Excerpt from the document:
This advisory circular (AC) sets forth suggestions and safety related recommendations to assist amateur and ultralight builders in developing individualized aircraft flight test plans.
The Federal Aviation Administration (FAA), the Experimental Aircraft Association (EAA), and the United States Ultralight Association (USUA) are concerned and committed to improving the safety record of amateur-built and ultralight aircraft.
To continue reading see the pdf below: