#include <bits/stdc++.h>
using namespace std;
void solve() {
  int n, k, i, len, j, size;
  cin >> n >> k;
  int arr[n];
  set<int> s;
  for (i = 0; i < n; i++) {
    cin >> arr[i];
    s.insert(arr[i]);
  }
  size = s.size();
  if (size > k)
    cout << "-1" << endl;
  else {
    len = n * k;
    cout << len << endl;
    for (j = 0; j < n; j++) {
      for (int p : s) cout << p << " ";
      for (i = 0; i < k - size; i++)
        cout << "2"
             << " ";
    }
    cout << endl;
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  ;
  int t;
  cin >> t;
  while (t--) solve();
  return 0;
}
