#include <bits/stdc++.h>
using namespace std;
void solve() {
  int n;
  cin >> n;
  string s;
  cin >> s;
  for (int i = 0; i < s.size(); i += 2) cout << s[i];
  cout << endl;
}
int main() {
  int t;
  for (scanf("%d", &t); t--;) {
    solve();
  }
  return 0;
}
