#include <bits/stdc++.h>
using namespace std;
#define rep(i, x, limit) for (int i = (int)x; i < (int)limit; i++)
#define REP(i, x, limit) for (int i = (int)x; i <= (int)limit; i++)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define el '\n'
#define spa " "
#define Yes cout << "Yes" << el
#define No cout << "No" << el
#define YES cout << "YES" << el
#define NO cout << "NO" << el
#define eps (1e-10)
#define Equals(a,b) (fabs((a) - (b)) < eps )
#define debug(x) cerr << #x << " = " << x << el
using ll = long long;
using ull = unsigned long long;
using pii = pair<int,int>;
using pll = pair<ll,ll>;
using vi = vector<int>;
using vl = vector<ll>;
using vvl = vector<vector<ll>>;
using vs = vector<string>;
using vb = vector<bool>;
const double pi = 3.141592653589793238;
const int inf = 1073741823;
const ll infl = 1LL << 60;
const string ABC = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
const string abc = "abcdefghijklmnopqrstuvwxyz";
const ll MOD = 998244353;
#include<atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using vm = vector<mint>;
string FG(ll n,string ss){
  string s=ss;
    if(n==1)return "B";
    string stc="AB";
    rep(i,0,n-2)stc+="A";
    ll wc=0;
    rep(i,0,n){
      if(wc==0){
        if(stc[i]!=s[i]){
          wc++;
          s[i]=stc[i];
        }
      }else{
        if(stc[i]==s[i])break;
        else s[i]=stc[i];
      }
    }
    s[0]='B';
    return s;
  }

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  ll t;cin>>t;
  while(t--){
    ll n;string s;cin>>n>>s;
    cout<<FG(n,s)<<el;
  }
}