#include<cstdio>
#include<iostream>
#include<cstdlib>
#include<cmath>
#include<algorithm>
#include<cstring>
#include<map>
#include<vector>
#include<queue>
#include<iterator>
#define dbg(x) cout<<#x<<" = "<<x<<endl;
#define INF 0x3f3f3f3f
#define LLINF 0x3f3f3f3f3f3f3f3f
#define eps 1e-6
 
using namespace std;
typedef long long LL;
typedef pair<int, int> P;
const int maxn = 200100;
const int mod = 998244353;
char str[maxn];

int main()
{
    int t, n, m, i, j,k;
    scanf("%d", &t);
    while(t--){
        scanf("%d %s", &n, str);
        sort(str, str+n);
        printf("%s\n", str);
    }
    return 0;
}