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

int main(int argc, char const *argv[])
{
// #ifndef ONLINE_JUDGE
// 	freopen("input.txt", "r", stdin);
// 	freopen("output.txt", "w", stdout);
// #endif

	ll tc;
	cin >> tc;
	while (tc--) {
		ll n;
		string str;
		cin >> n;
		cin >> str;
		sort(str.begin(), str.end());
		cout << str << endl;

	}


	return 0;
}
