The stat function can give you that information. Additionally, thanks to pileofrogs, Test::File has owner_is and owner_isnt function. Even if you don't want to use the module, you can look at the code. Those functions handle either the numeric UID or the name version. Although they are for users, the group stuff works in much the same way (and pileofrogs actually has the patch I need to apply to get the group equivalents.

The stat and chown functions will need the numeric versions, which you can get with getgrnam if you have the name (although I'm not sure how this works on Windows.) The first argument to chown is the owner, and the second is the group.