#include<bits/stdc++.h>
using namespace std;

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