I have yet to see an entry/transit test requirement which requires a doctor's review or approval. It is the test result, not the diagnosis, which is of interest to border authorities.
However, it is important to check the requirements of the specific entry/transit country(ies) as some of them have very specific requirements which may make sense to the countries in terms of their local medical community, but make little sense in the context of the country in which the test is taken. These include certifications with stamps, passport numbers to match and so on,