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

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