T = int(input())
for _ in range(T):
    N = int(input())
    S = input()
    ans = []
    NA, NB = 0, 0
    for s in reversed(S):
        if s == "A":
            if NB == 0:
                ans.append("A")
            elif NB == 1:
                ans.append("AB")
                NB -= 1
            else:
                NB -= 1
        else:
            NB += 1
    ans += ["B"] * NB
    ans.reverse()
    print("".join(ans))