#include <bits/stdc++.h>
using namespace std;
void solve() {
  int n, k;
  cin >> n >> k;
  vector<int> a(n);
  set<int> d;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    d.insert(a[i]);
  }
  if (d.size() > k)
    cout << -1 << endl;
  else {
    cout << n * k << endl;
    set<int>::iterator it;
    vector<int> b;
    for (it = d.begin(); it != d.end(); it++) b.push_back(*it);
    while (b.size() < k) b.push_back(1);
    for (int i = 0; i < n; i++)
      for (int j = 0; j < k; j++) cout << b[j] << " ";
    cout << endl;
  }
}
int main() {
  int t;
  cin >> t;
  while (t--) solve();
  return 0;
}
