for _ in range(int(input())):
    N = int(input())
    S = list(input())

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