#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  int t;
  cin >> t;
  while (t--) {
    int n, m;
    cin >> n >> m;
    vector<long long> v(n);
    for (int i = 0; i < n; i++) {
      string s;
      cin >> s;
      long long a = 0;
      for (int j = 0; j < m; j++) {
        if (s[j] == '1') {
          a += (1LL << (m - 1 - j));
        }
      }
      v[i] = a;
    }
    sort(v.begin(), v.end());
    long long mid = (1LL << (m - 1)) - 1;
    long long x = (1 << m);
    for (int i = 0; i < n; i++) {
      if (v[i] < mid) {
        if (x % 2 == 0) mid++;
        x--;
      } else if (v[i] == mid) {
        if (x % 2 == 0) {
          mid++;
          x--;
        } else {
          long long q = mid - 1;
          int y;
          while (1) {
            y = 0;
            for (int j = 0; j < n; j++) {
              if (q == v[j]) {
                q--;
                y = 1;
                break;
              }
            }
            if (!y) break;
          }
          mid = q;
          x--;
        }
      } else {
        if (x % 2) {
          long long q = mid - 1;
          int y;
          while (1) {
            y = 0;
            for (int j = 0; j < n; j++) {
              if (q == v[j]) {
                q--;
                y = 1;
                break;
              }
            }
            if (!y) break;
          }
          mid = q;
        }
        x--;
      }
    }
    for (int j = m - 1; j >= 0; j--) {
      if (mid & (1LL << j)) {
        cout << 1;
      } else
        cout << 0;
    }
    cout << endl;
  }
}
