#include <bits/stdc++.h>
using namespace std;
char B[200];
int main() {
  int t;
  scanf("%d", &t);
  while (t--) {
    int n;
    scanf("%d", &n);
    string A;
    cin >> A;
    int k = 0;
    for (int i = 0; i < n; i++) B[i] = A[i + (k++)];
    B[n] = '\0';
    cout << B << endl;
  }
}
