#include <iostream>
#include <algorithm>
#include <string>
using namespace std;
int main()
{
	int t, n;
	string s, b = "trygub";
	cin >> t;
	while (t--)
	{
		int k = 0;
		cin >> n >> s;
		sort(s.begin(), s.end());
		cout << s << endl;
	}
}