#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void swap(char* a, char* b) {
    char temp = *a;
    *a = *b;
    *b = temp;
}

void sort(char* word) {
    for (unsigned int i = 0; i < strlen(word)-1; ++i) {
        for (unsigned int j = i+1; j < strlen(word); ++j) {
            if (word[i] > word[j]) {
                swap(&word[i], &word[j]);
            }
        }
    }
}

int main() {
    int tt;
    scanf("%d", &tt);
    while (tt--) {
        int n;
        scanf("%d", &n);
        char s[n];
        scanf("%s", s);
        sort(s);
        printf("%s\n", s);
    }
}