T = int(input())
for _ in range(T):
    N = int(input())
    S = list(input())
    if N<=2:
        print('B'*N)
    else:
        if ''.join(S[:3]) != 'BBB':
            S[0]='B'
            S[1]='B'
            S[2]='A'
        print(''.join(S))