Not really, its just that it won't be recognized as evidence nor attenuating circumstances if the man become violent and kill or disfigure his partner. It is illegal to provide the test mind you, not to ask for it.
So the reason why it is illegal to provide the test is medical data protection. France is really high on this, the restrictions on processing medical data like diabetes, asthma are probably the strictest in europe - probably for historical/cultural reasons, but i'm not sure and only have circumstential evidence of this (and btw, with the americanisation/globalisation of french society, those cultural reasons will disapear).
The genitical data are even more protected.
And by the way, for us (or at least for people from brittany, i don't know that much people elsewhere), being a father or a grandfather is'nt a genetical thing. The man who share 1/4 of my genes with i call Warren, the one who raised my father and me i used to call grandfather (well, more endearingly than that)
It is not.
https://www.francepaternite.com/est-il-legal-de-realiser-un-...