def main():
	t = int(input())
	for _ in range(t):
		solve()
		
		
def solve():
	n = int(input())
	s = list(input())
	for i, c in enumerate(s):
		if i&1:
			if s[i]=="A":
				s[i] = "B"
				break
			elif s[i]=="B":
				s[i] = "C"
			else:
				break
		elif s[i]=="C":
			s[i] = "A"
		else:
			break
	print("".join(s))
	
	
if __name__ == "__main__":
	main()