
// Problem : A. Avoid Trygub
// Contest : Codeforces - Codeforces Global Round 12
// URL : https://codeforces.com/contest/1450/problem/A
// Memory Limit : 256 MB
// Time Limit : 1000 ms
// Powered by CP Editor (https://github.com/cpeditor/cpeditor)

#include<bits/stdc++.h>
#include<set>
#define lli long long int
#define pb push_back
#define cio ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL)
#define rep(i,a,n) for(i=a;i<n;i++)
#define all(v) (v.begin(),v.end())
#define ppb pop_back
#define vsz v.size()
#define pi 3.141592653589793238
using namespace std;
int main()
{
	lli t,n,i;
	cin>>t;
	while(t--){
		cin>>n;
		string s;
		cin>>s;
		sort all(s);
		cout<<s<<endl;
	}
	return 0;
}