Ireland boss Declan Kidney has been forced to make five changes to his injury-hit line-up that will start at Murrayfield this weekend.
But he has surprised many by opting against selecting the out-of-form – yet highly experienced – Ronan O'Gara and instead picking Ulster fly-half Paddy Jackson for his first cap.
Ulster centre Luke Marshall will also make his first Ireland appearance as Kidney adjusts his squad due to injuries and suspension.
Johnson, on the other hand, makes just one alteration to his starting XV following their 34-10 victory over Italy, replacing tighthead prop Euan Murray – who refuses to play on Sundays on religious grounds – with Geoff Cross.
Johnson said: "We know the players coming in. Their form regionally has been superb and these kids are good players.
"Sometimes what happens is that (people) expect the 'known names' to be a massive, massive loss. But what (people) probably don't know is the 'no names' and how good they are.
"This is a genuine Test match, a quality Test match against a formidable opposition who will come here buoyed by years of achievement here.
"We understand what we are up against – we are not deluding ourselves – and we understand that what was good enough against Italy won't be good enough against Ireland."
Johnson added: "We have got the ability and potential in this side to hurt some teams but we have got to do it consistently. It was one win but let's not get carried away with it."