#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  while (t--) {
    int N;
    string S;
    cin >> N >> S;
    vector<int> c(N + 1, 0);
    int x = N - 1;
    while (0 < x && S[x] == 'A') {
      x--;
    }
    for (int i = x; i > 0; i--) {
      c[i - 1] = c[i];
      if (S[i] == 'A') {
        c[i - 1]--;
      } else {
        c[i - 1]++;
      }
    }
    int cnt = 0;
    for (int i = 0; i < N; i++) {
      if (S[i] == 'A') {
        if (c[i] <= 1) {
          cout << 'A';
        } else {
          cnt++;
        }
      } else {
        if (cnt > 0) {
          cnt--;
        } else {
          cout << 'B';
        }
      }
    }
    cout << endl;
  }
}