for _ in range(int(input())):
  n=int(input())
  s=[*input()]
  if s[0]=='A':
    print(*s,sep='')
    continue
  a=0
  for i in range(n):
    if a==0:
      if s[i]!='A':
        s[i]='A'
        a=1
        continue
      else:
        break
    else:
      if s[i]!='C':
        s[i]='C'
        break
  print(*s,sep='')