#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  while (t != 0) {
    t--;
    int n;
    cin >> n;
    char s[2 * n - 1], w[n];
    int i;
    for (i = 1; i <= 2 * n - 1; i++) {
      cin >> s[i];
    }
    for (i = 1; i <= n; i++) {
      w[i] = s[2 * i - 1];
    }
    for (i = 1; i <= n; i++) {
      cout << w[i];
    }
    cout << endl;
  }
}
