def solve():
    N = int(input())
    cs = list(input())
    for i in range(N):
        if i % 2 == 0:
            if cs[i] == 'C':
                cs[i] = 'A'
            else:
                break
        else:
            if cs[i] == 'A':
                cs[i] = 'B'
                break
            elif cs[i] == 'B':
                cs[i] = 'C'
            else:
                break

    return ''.join(cs)


INF = 1 << 60
T = int(input())
for _ in range(T):
    ans = solve()
    print(ans)