import sys
input = sys.stdin.readline

T=int(input())

for tests in range(T):
    N=int(input())
    S=list(input().strip())

    if N==1:
        print("B")
        continue
    if N==2:
        print("BB")
        continue

    if S[:2]==["B","B"]:
        print("".join(S))
        continue

    if S[:2]==["A","A"] or S[:2]==["B","A"]:
        for i in range(2,N):
            if S[i]=="B":
                S[i]="A"
            else:
                break

        S[0]="B"
        S[1]="B"

        print("".join(S))

    else:
        flag=0
        for i in range(2,N):
            if S[i]=="B":
                flag=1
                S[i]="A"
            elif S[i]=="A" and flag==1:
                break

        S[0]="B"
        S[1]="B"

        print("".join(S))