#include <bits/stdc++.h>
using namespace std;
typedef unsigned long long ull;

int main() {
  int t;
  cin >> t;
  while (t--) {
    int n; cin >> n;
    vector<char> s(n);
    for (int i = 0; i < n; i++) cin >> s[i];

    sort(s.begin(), s.end());

    for (int i = 0; i < n; i++) {
      cout << s[i];
    }
    cout << endl;
  }


  return 0;
}
