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

def solve():
    _ = input()
    s = list(input())
    if len(s)==1:
        print("B")
        return
    elif len(s)==2:
        print("BB")
        return
    if s[0]==s[1]==s[2]=="A":
        s[0] = s[1] = "B"
    elif s[0]=="A":
        rle = []
        pre = s[0]
        cnt = 0
        for c in s:
            if pre==c:
                cnt += 1
            else:
                rle.append((pre, cnt))
                pre = c
                cnt = 1
        rle.append((pre, cnt))
        if rle[1][1] > 1:
            l = rle[0][1]+2
            r = rle[0][1]+rle[1][1]
            for i in range(l, r):
                s[i] = "A"
        elif len(rle) > 3:
            l = rle[0][1]+rle[1][1]+rle[2][1]
            r = l+rle[3][1]
            for i in range(l, r):
                s[i] = "A"
        for i in range(rle[0][1]):
            s[i] = "B"
    else:
        f = -1
        for i in range(len(s)):
            if s[i]=="B":
                f = i
                if f >= 0:
                    break
        while f < len(s) and s[f]=="B":
            s[f] = "A"
            f += 1
    print("".join(s))


if __name__ == "__main__":
    main()