#include <bits/stdc++.h>
using namespace std;
const long long int INF = 9223372036854775807;
const long long int mod = 1e9 + 7;
#pragma GCC target("avx2")
#pragma GCC optimization("unroll-loops")
int MOD(int a, int b) {
  if (a > b)
    return a - b;
  else
    return b - a;
}
long long int max3(long long int a, long long int b, long long int c) {
  return max(c, max(a, b));
}
long long int min3(long long int a, long long int b, long long int c) {
  return min(a, min(b, c));
}
long long int power(long long int x, long long int y, long long int mod1) {
  long long int res = 1;
  while (y > 0) {
    if (y & 1) res = (res * x);
    y = y >> 1;
    x = (x * x);
  }
  return res;
}
long long int logg(long long int a) {
  long long int x = 0;
  while (a > 1) {
    x++;
    a /= 2;
  }
  return x;
}
long long int gcd(long long int a, long long int b) {
  if (a == 0) return b;
  return gcd(b % a, a);
}
long long int abso(long long int x) {
  if (x < 0) {
    return -x;
  }
  return x;
}
long long int ceiling(long long int a, long long int b) {
  if (a % b == 0) {
    return a / b;
  } else {
    return a / b + 1;
  }
}
long long int modinv(long long int x, long long int p) {
  return power(x, p - 2, p);
}
struct point {
  long long int x;
  long long int y;
};
long long int cross(point a, point b) { return a.x * b.y - b.x * a.y; }
bool ccw(point p1, point p2) {
  if (cross(p1, p2) > 0) {
    return true;
  } else {
    return false;
  }
}
void ccw_sort(vector<point> &v) {
  vector<point> v1, v2;
  for (int i = 0; i < v.size(); i++) {
    if (v[i].y > 0) {
      v1.push_back(v[i]);
    } else {
      v2.push_back(v[i]);
    }
  }
  sort(v1.begin(), v1.end(), ccw);
  sort(v2.begin(), v2.end(), ccw);
  for (int i = 0; i < v2.size(); i++) {
    v1.push_back(v2[i]);
  }
  v = v1;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  ;
  int t;
  cin >> t;
  while (t--) {
    long long int n, m;
    cin >> n >> m;
    vector<long long int> a(n);
    for (int i = 0; i < n; i++) {
      string str;
      cin >> str;
      a[i] = stoll(str, NULL, 2);
    }
    long long int ans =
        (long long int)((long long int)1 << ((long long int)m - 1)) - 1;
    for (long long int j = -2 * n; j <= 2 * n; j++) {
      long long int cur =
          (long long int)((long long int)1 << (long long int)(m - 1)) - 1 + j;
      bool c = true;
      long long int less = 0;
      long long int great = 0;
      if (cur < 0) {
        continue;
      }
      for (int k = 0; k < n; k++) {
        if (a[k] == cur) {
          c = false;
          break;
        } else {
          if (a[k] < cur) {
            less++;
          } else {
            great++;
          }
        }
      }
      long long int left = cur + 1 - less;
      long long int right =
          ((long long int)1 << (long long int)m) - 1 - cur - great;
      if (c && (left == right || left == right + 1)) {
        ans = cur;
        break;
      }
    }
    string gg;
    for (int j = 0; j < m; j++) {
      gg.push_back('0' + (ans % 2));
      ans = ans / 2;
    }
    reverse(gg.begin(), gg.end());
    cout << gg << endl;
  }
}
