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

#define endl            "\n"
#define int             long long
#define mod             1000000007
#define inf             1e18
#define w(t)            int t; cin>>t; while(t--)

void c_p_c()
{
	ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#ifndef ONLINE_JUDGE
	freopen("input.txt", "r", stdin);
	freopen("output.txt", "w", stdout);
#endif
}
int32_t main() {
	c_p_c();
	w(t) {
		int n;
		cin >> n;
		string s;
		cin >> s;
		sort(s.begin(), s.end());
		cout<<s<<endl;
	}
	return 0;
}