Best Enemies

import java.io.*;
import java.util.*;
import static java.lang.System.*;
import static java.lang.Math.*;
class Code
{

    void run() {
        int tc=ni();
        StringBuilder sb=new StringBuilder();
        while(tc-->0) {
            int n=ni();
            String s=ns(); ni();
            int fr[] = new int[10];
            for(int i=0;i<n;i++) fr[s.charAt(i)-'0']++;
            int j=0;
            xD:
            for(int i=9;i>0;i++) {
                while(fr[i]>0) {
                    int x=s.charAt(j)-'0';
                    if(x==i) fr[i]--;
                    else {
                        sb.append(i); j++;
                        while(j<n) {
                            if(s.charAt(j)-'0'==x) { sb.append(x); x=-1; }
                            else sb.append(s.charAt(j));
                            j++;
                        }
                        break xD;
                    }
                    sb.append(x);
                    j++;
                }
            }
            sb.append("\n");
        }
        out.println(sb);
        out.flush();
        out.close();
    }

    public static void main(String[] args)throws IOException {
        try {
            new Code().run();
        } catch(Exception e) {}
    }

    FastReader sc = new FastReader();
    PrintWriter out = new PrintWriter(System.out);

    String ns() { return sc.next(); }
    int ni() { return sc.nextInt(); }
    long nl() { return sc.nextLong(); }
    int[] ni(int n) {
        int a[]=new int[n];
        for(int i=0;i<n;a[i++]=ni());
        return a;
    }
    long[] nl(int n) {
        long a[]=new long[n];
        for(int i=0;i<n;a[i++]=nl());
        return a;
    }

    int[][] ni(int n,int m) {
        int a[][]=new int[n][m];
        for(int i=0;i<n;i++)
            for(int j=0;j<m;j++)
                a[i][j]=ni();
        return a;
    }
    long[][] nl(int n,int m) {
        long a[][]=new long[n][m];
        for(int i=0;i<n;i++)
            for(int j=0;j<m;j++)
                a[i][j]=nl();
        return a;
    }
    int gcd(int a, int b) {
        return b==0?a:gcd(b,a%b);
    }
    static class FastReader {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;
        private FastReader.SpaceCharFilter filter;
        FastReader(){ this(System.in); }
        public FastReader(InputStream stream) {
            this.stream = stream;
        }

        public int read() {
            if (numChars == -1) throw new InputMismatchException();
            if (curChar >= numChars) {
                curChar = 0;
                try {
                    numChars = stream.read(buf);
                } catch (IOException e) {
                    throw new InputMismatchException();
                }
                if (numChars <= 0) return -1;
            }
            return buf[curChar++];
        }

        public int nextInt() {
            int c = read();
            while (isSpaceChar(c)) c = read();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            int res = 0;
            do {
                if (c < '0' || c > '9') throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            }
            while (!isSpaceChar(c));
            return res * sgn;
        }

        public long nextLong() {
            int c = read();
            while (isSpaceChar(c)) c = read();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            long res = 0;
            do {
                if (c < '0' || c > '9') throw new InputMismatchException();
                res = res*1L*10;
                res += c - '0';
                c = read();
            }
            while (!isSpaceChar(c));
            return res *1L* sgn;
        }

        public String next() {
            int c = read();
            while (isSpaceChar(c)) c = read();
            StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = read();
            } while (!isSpaceChar(c));
            return res.toString();
        }

        public boolean isSpaceChar(int c) {
            if (filter != null) return filter.isSpaceChar(c);
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }

        public interface SpaceCharFilter {
            public boolean isSpaceChar(int ch);

        }

    }

}