#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t;
  cin >> t;
  while (t--) {
    int n, k;
    int a[110];
    cin >> n >> k;
    set<int> dif;
    for (int i = 0; i < n; i++) {
      cin >> a[i];
      dif.insert(a[i]);
    }
    if (dif.size() > k) {
      cout << "-1" << endl;
      continue;
    }
    cout << k * n << endl;
    set<int>::reverse_iterator o = dif.rbegin();
    for (int i = 0; i < n; i++) {
      set<int>::reverse_iterator o = dif.rbegin();
      int z = k;
      int up = 1;
      while (z--) {
        cout << *o << " ";
        if (up)
          o++;
        else
          o--;
        if (o == dif.rend()) {
          up = 0;
          o--;
          o--;
        }
        if (o == dif.rbegin()) up = 1;
      }
    }
    cout << endl;
  }
  return 0;
}
