import sys
input = sys.stdin.readline
T = int(input())
for _ in range(T):
    N = int(input())
    S = input().strip()
    if N==1:
        print("B")
        continue
    if S[0]=="A":
        if S[1]=="A":
            ans = ["BB"]
            idx = 1
            for i in range(2, N):
                if S[i]=="A":
                    break
                ans.append("A")
                idx = i
            for i in range(idx+1, N):
                ans.append(S[i])
            print("".join(ans))
        else:
            ans = ["BB"]
            idx = 1
            for i in range(2, N):
                if S[i]=="B":
                    break
                ans.append("A")
                idx = i
            for i in range(idx+1, N):
                if S[i]=="A":
                    break
                ans.append("A")
                idx = i
            for i in range(idx+1, N):
                ans.append(S[i])
            print("".join(ans))
    else:
        if S[1]=="A":
            ans = ["BB"]
            idx = 1
            for i in range(2, N):
                if S[i]=="A":
                    break
                ans.append("A")
                idx = i
            for i in range(idx+1, N):
                ans.append(S[i])
            print("".join(ans))
        else:
            ans = ["BB"]
            for i in range(2, N):
                ans.append(S[i])
            print("".join(ans))