T = int(input())

for _ in range(T):
    N = int(input())
    S = input()
    
    ans = []
    left = 0
    while left < N:
        right = left
        count = 0
        while right < N and count <= 0:
            if S[right] == "A":
                count -= 1
            else:
                count += 1
            right += 1
        if count <= 0:
            ans.append(S[left:right])
            left = right
        else:
            ans.append("B")
            left = right
    print("".join(ans))