Will testdisk undelete write over deleted files?

I have an external drive that I accidentally deleted a lot of files off of. I can still see all the files in testdisk and have the option to undelete everything, but will recovering the files onto the same drive possibly cause an issue? I don't know how testdisk (or really drive writing at all) works so I'm not sure if the recovery process could possibly end up writing over the other undeleted files on the drive (meaning I'd only get some files back) or if I'm safe to recover to the same drive I deleted the files off of.