T = int(input())
for _ in range(T):
    N = int(input())
    S = input()
    res = []
    for i, c in enumerate(S):
        if i % 2 == 0: # Alice
            if c == 'C':
                res.append('A')
            else:
                res.append(S[i:])
                break
        else: # Bob
            if c == 'A':
                res.append('B')
            elif c == 'B':
                res.append('C')
            else:
                res.append(S[i:])
                break
    print(*res, sep="")