#include <bits/stdc++.h>
using namespace std;
int main() {
  int tc;
  scanf("%d", &tc);
  while (tc--) {
    int n;
    scanf("%d", &n);
    char arr[2 * n + 1];
    scanf("%s", arr);
    int j = 0;
    for (int i = 0; i < n; i++) {
      cout << arr[i + j];
      j++;
    }
    printf("\n");
  }
}
