#include<bits/stdc++.h>

using namespace std;
#define int long long

int32_t main()
{
    int t;
    cin >> t;
    while(t--)
    {
        string s;
        int n;
        cin >> n;
        cin >> s;
        sort(s.begin(),s.end());
        cout << s << endl;
    }
    return 0;
}
