#include <bits/stdc++.h>
using namespace std;
int t;
int n;
char a[104];
int main(void) {
  cin >> t;
  for (int c1 = 0; c1 < t; c1++) {
    cin >> n;
    for (int c2 = 0; c2 < n * 2 - 1; c2++) {
      cin >> a[c2];
    }
    for (int c2 = 0; c2 < n; c2++) {
      cout << a[c2 * 2];
    }
    cout << endl;
  }
  return 0;
}
