#include <bits/stdc++.h>

#define ll long long
// #define int ll
#define pii pair<int, int>
#define mp make_pair
#define vi vector<int>


using namespace std;

int main(int argc, char const *argv[]){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int t;
    cin >> t;
    while(t--){
        int n;
        string s;
        cin >> n >> s;
        sort(s.begin(), s.end());
        cout << s << endl;
    }
    return 0;
}
