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


def solve():
    n = int(input())
    s = list(input())
    rle = []
    fc = s[0]
    fn = 0
    for i in range(n):
        if s[i]==fc:
            fn += 1
        else:
            rle.append((fc, fn))
            fc = s[i]
            fn = 1
    rle.append((fc, fn))
    fc, fn = rle[0]
    if fc == "A":
        if fn <= 2:
            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
        for i in range(min(2, fn)):
            s[i] = "B"
    elif fn == 1 < n:
        s1, c1 = rle[1]
        if c1 <= 2:
            f = -1
            for i in range(1, 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
        for i in range(1, min(n, 3)):
            if s[i] == "B": break
            s[i] = "B"
    print("".join(s))


if __name__ == "__main__":
    main()