import sys
input = sys.stdin.readline

T=int(input())

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

    for i in range(N):
        if i%2==0:
            if S[i]=="A" or S[i]=="B":
                break
            S[i]="A"
        else:
            if S[i]=="A":
                S[i]="B"
            elif S[i]=="B":
                S[i]="C"
            else:
                break

    print("".join(S))