T = int(input())

for _ in range(T):
	N = int(input())
	S = input()
	ans = []
	for i in range(N):
		if S[i] == "A":
			ans.append(0)
		elif S[i] == "B":
			ans.append(1)
		else:
			ans.append(2)
	now = "Alice"
	least = 0
	keep = -1
	while True:
		if least == N:
			if now == "Bob" and keep != -1:
				ans[keep] = (ans[keep] + 1) % 3
			break
		if now == "Alice":
			if ans[least] == 2:
				ans[least] = 0
			else:
				break
			now = "Bob"
			least += 1
		if now == "Bob":
			if keep != -1:
				ans[keep] = (ans[keep] + 1) % 3
				keep = -1
			else:
				if ans[least] == 2:
					break
				if ans[least] == 0:
					keep = least
				ans[least] = (ans[least] + 1) % 3
				least += 1
			now = "Alice"
	ANS = []
	for i in range(N):
		if ans[i] == 0:
			ANS.append("A")
		elif ans[i] == 1:
			ANS.append("B")
		else:
			ANS.append("C")
	print("".join(ANS))