def main():
	for _ in range(int(input())):
		solve()
		
		
def solve():
	n = int(input())
	s = list(input())
	fc = s[0]
	fn = 0
	for i in range(n):
		if s[i]==fc:
			fn += 1 
		else:
			break
	if fc == "A":
		if fn <= 2:
			f = -1
			for i in range(n):
				if s[i]=="B":
					if f < 0:
						f = i 
					else:
						f = i 
						break
			else: f = -1
			if f >= 0:
				while f < n and s[f]=="B":
					s[f] = "A"
					f += 1 
		for i in range(min(2, fn)):
			s[i] = "B"
	elif fn == 1:
		for i in range(1,min(n,3)):
			if s[i]=="B": break
		s[i] = "B"
	print("".join(s))
	
if __name__ == "__main__":
	main()