#include <bits/stdc++.h>
using namespace std;
void solve() {
  int N, K;
  cin >> N >> K;
  set<int> s;
  for (int i = 0; i < N; i++) {
    int a;
    cin >> a;
    s.insert(a);
  }
  if (s.size() > K) {
    cout << -1 << endl;
    return;
  }
  cout << N * K << endl;
  for (int i = 0; i < N; i++) {
    for (int b : s) cout << b << ' ';
    for (int j = 0; j < K - (int)s.size(); j++) cout << 1 << ' ';
  }
  cout << endl;
}
int main() {
  int t;
  cin >> t;
  while (t--) solve();
}
