Thank you for your response!

I do understand that the testing can have a different meaning than according to European (or Western) standards. I'm not trying to condemn, absolutely not. I'm just hoping to find out what it would mean for a person who wants to marry, probably not knowing that he or she has a disease, and finding that out through a obliged test.
What you are telling about people being able to buy a certificate from the doctor is very interesting information indeed! Does this mean that these certificates do not cost a lot? Otherwise, how would poor(er) people be able to buy them?
And your last statement about not being able to rely on the certificate, is that unreliable tests in general or only unreliable certificates due to buying them?