T = int(input())

for _ in range(T):
	N = int(input())
	S = input()
	ans = []
	ok = 1
	for i in range(N):
		if ok == 0:
			ans.append(S[i])
			continue
		if i % 2 == 0:
			if S[i] == "C":
				ans.append("A")
			else:
				ok = 0
				ans.append(S[i])
		else:
			if S[i] == "C":
				ok = 0
				ans.append(S[i])
			else:
				if S[i] == "A":
					ans.append("B")
					ok = 0
				else:
					ans.append("C")
	print("".join(ans))