DNA tested for what, exactly? I guess things like fragmentary remains may not be human, but a full skull is not so easy to confuse for a donkey. Ethnicity would only be useful if the saint in question had origins that would be out of place in Italy or if they had a specific ethnicity(like St Peter's remains not having a Levantine origin).

Yes well there are other things you could do with a DNA genotype than tag ethnicity or confirm it's human. Specifically related to a similarity metric between genotypes (which is how we go about arriving at an ethnicity estimate)

For example

if said saint has any known living relatives (and we are certain of that), then this confirms the veracity of the relic.

if said saint has multiple relics of various body parts, we DNA test each one and examine concordance.

of course a DNA test may QC fail, not enough DNA, too low quality, etc. But if it passes then we potentially have dead to rights a confirmation or refutation of the relic. For this reason I expect the church would be quite recalcitrant to have it tested, because there is a possible outcome that the relic is revealed to be a fake

"Consistency" whatever that might be.

Dave Allen's great joke about the relics concerns a doubter pressing on why there were two skulls of different sizes attributed to Saint Placeholder.

The answer was straightforward enough;

this one is his skull taken from his concecrated tomb in the Abbey of Overthere,

and this was his skull from when he was a child.

Soviets did this in 1918-20, without DNA analysis, of course.

https://ru-wikipedia-org.translate.goog/wiki/%D0%9A%D0%B0%D0...

Older relics can be tested, but the Catholic church won't really allow it, e.g. San Gennaro's blood in Naples is a flask of red clotted liquid which melts during some ceremonies, and is quite likely not blood at all. But there's a massive community of believers and thus it will not be challenged by the church.

For more modern miracles and relics the church does have a tight grip, and famously one pope threw a whole bag of Christ teeth in the Tiber river, but many older things have been "grandfathered".