I knew you would ask something like that so I posted those pictures for you to review. Notice the panel lines? Prominent panels like that are the hallmark of a plane with no RAM applied. Compare those J-20 pictures to the F-117 pictures
The F-117 was nearly completely covered with a radar absorbing material which is laborious and expensive to maintain. After each mission, maintenance specialists closely examine the aircraft's special coating to identify any needed repairs. If required, coatings were reapplied, allowed to cure, and re-inspected.
The coatings are a major part of stealth. Note the smoothness. Does this advance your understanding of stealth
almface:
What the F117 used represents the first generation of operationally deployed RAM coatings. It gives a pretty, smooth finished because of its inefficiency. The RAM used on the F117 needed to be applied in relatively thick coats in order to achieve the desired effect, that accounts for the smoothness, as the thick coats obscures all details, but also meant it added a considerable amount of weight to the aircraft.
Modern RAM coatings can achieve the same if not better effect with far thinner coats, which is why can you see panels on the likes of the F22 and F35, as the picture Engineer already posted readily demonstrates.
It was reported that when the Chinese got examples of the RAM coating from the F117 down over Serbia, they were very surprised and disappointed because the RAM materials they were used to working with were considerable more advanced.
You even bringing up RAM on the prototypes is rather silly.
RAM is delicate and expensive to apply and maintain. There is little need or reason to apply it to prototypes in such early stages of flight testing.
If RAM is to be applied to an initial prototype, it would likely only be done on the static test airframe, as the coatings would last far longer since it won't be exposed to the wear and tear of regular maintenance, adjustments and fly testing, and also because they would be able to mount the prototype up for detailed RCS testing without having to dispute the flight testing.
