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