from collections import deque
import sys
sys.setrecursionlimit(10**6)


def find_abc(cs: list):
    a = deque()
    b = deque()
    c = deque()
    for i, x in enumerate(cs):
        if x == 'A':
            a.append(i)
        elif x == 'B':
            b.append(i)
        elif x == 'C':
            c.append(i)

    return a, b, c


def f(cs: list, a, b, c):
    ai = a.popleft() if a else INF
    bi = b.popleft() if b else INF
    ci = c.popleft() if c else INF

    if ci < ai and ci < bi:
        cs[c] = 'A'
        return g(cs, a, b, c)

    return cs


def g(cs: list, a, b, c):
    ai = a.popleft() if a else INF
    bi = b.popleft() if b else INF
    ci = c.popleft() if c else INF

    if ci < ai and ci < bi:
        return cs

    if a < b:
        cs[a] = 'B'
    elif b < INF:
        cs[b] = 'C'

    return f(cs, a, b, c)


def solve():
    N = int(input())
    S = input()
    cs = list(S)
    a, b, c = find_abc(cs)
    res = f(cs, a, b, c)
    return ''.join(res)


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