def main():
    for _ in range(int(input())):
        solve()


def solve():
    n = int(input())
    s = list(input())
    pre = s[0]
    num = 0
    for c in s:
        if pre==c:
            num += 1
        else: break
    if pre=="A":
        if num > 2:
            s[0] = s[1] = "B"
        elif num==2:
            if num < n:
                p = 2
                while p < n and s[p]=="B":
                    s[p] = "A"
                    p += 1
            s[0] = s[1] = "B"
        else:
            f = -1
            for i in range(n):
                if s[i] == "B":
                    if f < 0:
                        f = i
                    else:
                        f = i
                        break
            else:
                f = -1
            if f >= 0:
                while f < n and s[f] == "B":
                    s[f] = "A"
                    f += 1
            s[0] = "B"
    elif num == 1:
        if num < n:
            s[1] = "B"
            if 2 < n and s[2]=="B":
                f = 2
                while f < n and s[f]=="B":
                    s[f] = "A"
                    f += 1
    print("".join(s))


if __name__ == "__main__":
    main()