//#include <monsterenergy>
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
const int MAX = 1e9;
const int MIN = -1*1e9;
const ll MAXLL = 1e18;
const ll MINLL = -1*1e18;

int main()
{
    int T; cin >> T;
    for(int t = 0; t < T; t++)
    {
        int N; cin >> N;
        string S; cin >> S;

        auto solve = [&](int start_idx) {
            int cnt_A = 0;
            for(int i = start_idx; i < N; i++) {
                if(S[i] == 'A') cnt_A++;
                else break;
            }

            if(cnt_A >= 3) {
                if(start_idx + 1 < N) S[start_idx + 1] = 'B';
            } else {
                bool flag = false;
                bool active = false;
                for(int i = start_idx; i < N; i++) {
                    if(S[i] == 'B') {
                        if(!flag) {
                            flag = true;
                        } else {
                            S[i] = 'A';
                            active = true;
                        }
                    } else {
                        if(active) break;
                    }
                }
            }
        };

        if(S[0] == 'A') {
            solve(0);
        } else {
            // Check for leading Bs
            int cnt_B = 0;
            for(int i = 0; i < N; i++) {
                if(S[i] == 'B') cnt_B++;
                else break;
            }
            if(cnt_B == 1) {
                if(N > 1 && S[1] == 'A') {
                    solve(1);
                }
            }
        }
        S[0] = 'B';
        cout << S << endl;
    }
    return 0;
}