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[0] if a else INF
    bi = b[0] if b else INF
    ci = c[0] if c else INF

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

    return cs


def g(cs: list, a, b, c):
    ai = a[0] if a else INF
    bi = b[0] if b else INF
    ci = c[0] if c else INF

    if ci < ai and ci < bi:
        return cs

    if ai < bi:
        cs[ai] = 'B'
        a.popleft()
    elif bi < INF:
        cs[bi] = 'C'
        b.popleft()

    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)