So, I've seen these, but I don't actually know what it's for. Could someone explain what it does, please? Thanks.

Test kits test your pets for carries or hidden genes/mutations. (hidden = carried traits behind visible ones)

They also help see the mutations (along with everything above) while a pet is a hatchling, since mutations aren't visible when they're that young.

This is useful particularly for breeders who want to breed a certain trait. :)

Hope that helps!