#include <bits/stdc++.h>   using namespace std;   const long double pi = 3.14159265359;   inline long long add(long long a, long long b, long long m) {     if ((a + b) >= m) return (a + b) % m;     return a + b;   }   inline long long mul(long long a, long long b, long long m) {     if ((a * b) < m) return a * b;     return (a * b) % m;   }   long long power(long long x, long long y, long long m) {     long long res = 1;     x = x % m;     if (x == 0) return 0;     while (y > 0) {       if (y & 1) res = (res * x) % m;       y = y >> 1;       x = (x * x) % m;     }     return res;   }   long long gcd(long long a, long long b) {     if (b == 0) return a;     return gcd(b, a % b);   }   int main() {     ios_base::sync_with_stdio;     cin.tie(0);     cout.tie(0);     int t = 1, n;     cin >> t;     while (t--) {       string s;       cin >> n;       cin >> s;       string ans;       int i = 0;       for (; i < s.length(); i++) {         if (s[i] ==  0 ) {           ans.push_back(s[i]);         } else {           break;         }       }       string ans2;       for (int i = s.length() - 1; i > -1; i--) {         if (s[i] ==  1 ) {           ans2.push_back(s[i]);         } else {           break;         }       }       if (ans.length() + ans2.length() == s.length()) {         cout << s << endl;       } else         cout << ans <<  0  << ans2 << endl;     }     return 0;   }   