t = int(input())
while t:
	t -= 1
	
	n = int(input())
	s = input()
	
	if n == 1:
		print("B")
		continue
	if n == 2:
		print("BB")
		continue
	
	s = list(s)
	if (s[0] == "A") & (s[1] == "B"):
		l = 2
		s[0] = "B"
		while l < n:
			if s[l] == "A":
				l += 1
				continue
			r = l
			while r < n:
				if s[r] == "B":
					s[r] = "A"
					r += 1
					continue
				else:
					break
			break
			
	else:
		s[0] = "B"
		s[1] = "B"
		s[2] = "A"
	
	print("".join(s))