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] == s[1] == "B":
		pass
	elif (s[0] == "A") & (s[1] == "B") & (s[2] == "A"):
		s[0] = "B"
		i = 2
		while i < n:
			if s[i] == "A":
				i += 1
				continue
			while i < n:
				if s[i] == "B":
					s[i] = "A"
					i += 1
					continue
				else:
					break
			break
	else:
		s[0] = "B"
		s[1] = "B"
		if s[2] == "A":
			pass
		else:
			i = 2
			while i < n:
				if s[i] == "A":
					break
				else:
					s[i] = "A"
					i += 1
			

	print("".join(s))