T = int(input())
for _ in range(T):
    N = int(input())
    S = list(input())
    B_count = 0
    ans = [S[-1]]
    if S[-1] == "B":
        B_count+=1
    A_count = 0
    for i in range(-2,-(N+1),-1):
        if S[i] == "B":
            B_count+=1
            ans.append("B")
        else:
            if B_count>A_count+1 and ans[-1]=="B":
                ans.pop()
                B_count-=1
                if B_count == 0:
                    A_count = 0
            else:
                ans.append("A")
                if B_count >=1:
                    A_count += 1
    print("".join(reversed(ans)))