#include <bits/stdc++.h>
using namespace std;
int a[109], d[109];
int main() {
  ios::sync_with_stdio(0);
  long long t;
  cin >> t;
  while (t--) {
    long long k, n;
    for (int i = 0; i < 109; i++) d[i] = 0;
    cin >> n >> k;
    vector<int> u;
    for (int i = 0; i < n; i++) {
      cin >> a[i];
      d[a[i]]++;
      if (d[a[i]] == 1) u.push_back(a[i]);
    }
    if (u.size() > k) {
      cout << -1 << endl;
      continue;
    }
    while (u.size() < k) u.push_back(1);
    long long ans = k * n;
    cout << ans << endl;
    for (int i = 0; i < n; i++)
      for (int j = 0; j < u.size(); j++) cout << u[j] << " ";
    cout << endl;
  }
  return 0;
}
