Further, it says that F35 is the first nuclear capable Gen 5 fighter ever. If it means what I think it does, neither China nor Russia have figured a way to put nukes on their fifth gen fighters, and those guys are not known for being overly cautious when they are behind in arms race.
> The B61 has been deployed by a variety of US military aircraft. US aircraft cleared for its use have included the B-1 Lancer, B-2 Spirit, B-52 Stratofortress, F/A-18 Hornet, A-6 Intruder, A-4 Skyhawk, F-111, F-15E Strike Eagle and F-16 Fighting Falcon and the F-35A. As part of NATO Nuclear Weapons Sharing, German and Italian Panavia Tornado aircraft can also carry B61s. The B61 can fit inside the F-22 Raptor's weapons bays and will also be carried by the Lockheed Martin F-35 Lightning II.
But presumably the bomb has some mount and you would want to validate that and the bomb door/release mechanism. You probably also have some sort of targeting system, guidance control, arming system to integrate all which probably require some sort of validation.
You would probably also want certification to validate the operational characteristics of the aircraft carrying the bomb, e.g. range, flight performance, detection, capacity.
And seriously, it is a nuke, better safe than sorry. If you can test it ahead of time you do that.