from collections import deque, defaultdict, Counter
from bisect import bisect_left, bisect_right
from itertools import permutations, combinations
from heapq import heappop, heappush
import math, sys
input = lambda: sys.stdin.readline().rstrip("\r\n")
_int = lambda x: int(x)-1
MOD = 998244353 #10**9+7
INF = 1<<60
Yes, No = "Yes", "No"

T = int(input())
for _ in range(T):
    N = int(input())
    S = list(input())
    for i in range(2):
        if i%2:
            if S[i] != "C":
                S[i] = chr(ord(S[i])+1)
            else: break
        else:
            if S[i] == "C":
                S[i] = "A"
            else: break
    print(*S, sep="")