#include <bits/stdc++.h>
const int LG = 21;
const int FN = 400005;
const long long MOD = 1e9 + 7;
const long long INF = 1e9;
const long long INFLL = 1e18;
using namespace std;
int cx[4] = {-1, 0, 1, 0};
int cy[4] = {0, -1, 0, 1};
long long inq(long long x, long long y) {
  if (!y) return 1 % MOD;
  long long l = inq(x, y / 2);
  if (y % 2) return l * l % MOD * x % MOD;
  return l * l % MOD;
}
long long rev(long long x) { return inq(x, MOD - 2); }
bool __precomputed_combinatorics = 0;
vector<long long> __fact, __ufact, __rev;
void __precompute_combinatorics() {
  __precomputed_combinatorics = 1;
  __fact.resize(FN);
  __ufact.resize(FN);
  __rev.resize(FN);
  __rev[1] = 1;
  for (int i = 2; i < FN; i++)
    __rev[i] = MOD - __rev[MOD % i] * (MOD / i) % MOD;
  __fact[0] = 1, __ufact[0] = 1;
  for (int i = 1; i < FN; i++)
    __fact[i] = __fact[i - 1] * i % MOD,
    __ufact[i] = __ufact[i - 1] * __rev[i] % MOD;
}
long long fact(int x) {
  if (!__precomputed_combinatorics) __precompute_combinatorics();
  return __fact[x];
}
long long cnk(int n, int k) {
  if (k < 0 || k > n) return 0;
  if (!__precomputed_combinatorics) __precompute_combinatorics();
  return __fact[n] * __ufact[n - k] % MOD * __ufact[k] % MOD;
}
void solve() {
  long long n, m;
  cin >> n >> m;
  vector<long long> a;
  for (int i = 0; i < n; i++) {
    string s;
    cin >> s;
    long long k = 0;
    for (int j = 0; j < m; j++) {
      k = 2 * k + s[j] - '0';
    }
    a.push_back(k);
  }
  long long c = (1LL << m) - n;
  sort((a).begin(), (a).end());
  long long ex = (c - 1) / 2;
  for (int i = 0; i < a.size(); i++) {
    if (a[i] <= ex) ex++;
  }
  vector<long long> ans;
  for (int i = 0; i < m; i++) {
    ans.push_back(ex % 2);
    ex /= 2;
  }
  reverse((ans).begin(), (ans).end());
  for (int i = 0; i < m; i++) {
    cout << ans[i];
  }
  cout << "\n";
}
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int t;
  cin >> t;
  while (t--) {
    solve();
  }
}
