#include <bits/stdc++.h>
using namespace std;
signed solve() {
  long long n, k;
  cin >> n >> k;
  set<long long> s;
  long long v;
  for (long long i = 0; i < n; ++i) {
    cin >> v;
    s.insert(v);
  }
  if ((long long)s.size() <= k) {
    cout << n * k << '\n';
    for (long long i = 0; i < n; i++) {
      for (auto &x : s) cout << x << " ";
      for (long long i = 0; i < k - (long long)s.size(); i++) cout << 1 << " ";
    }
  } else {
    cout << -1;
  }
  cout << '\n';
  return 0;
}
signed main() {
  ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  long long t = 1;
  cin >> t;
  while (t--) solve();
  return 0;
}
