def solve():
    N = int(input())
    S = list(input())

    if N == 1:
        print("B")
        return

    def flip(l, r):
        nonlocal S
        for i in range(l, r):
            if S[i] == "A":
                S[i] = "B"
            else:
                S[i] = "A"

    if S[:2] == ["B", "B"]:
        flip(0, 1)

    elif S[:2] == ["A", "B"]:
        left, right = None, N
        for i in range(2, N):
            if left is None and S[i] == "B":
                left = i

            if left is not None and S[i] == "A":
                right = i
                break

        if left is not None:
            flip(left, right)

    else:
        right = N
        for i in range(2, N):
            if S[i] == "A":
                right = i
                break

        if S[0] == "A":
            flip(1, right)
        else:
            flip(0, right)

    flip(0, 1)

    print(*S, sep="")


if __name__ == "__main__":
    T = int(input())

    for _ in range(T):
        solve()