def solve():
    N = int(input())
    S = [s for s in input()]

    for i in range(N):
        if i % 2 == 0:
            if S[i] == "C":
                S[i] = "A"
            else:
                break
        else:
            if S[i] == "A":
                S[i] = "B"
                break
            elif S[i] == "B":
                S[i] = "C"
            else:
                break

    print(*S, sep="")


if __name__ == "__main__":
    T = int(input())

    for _ in range(T):
        solve()