#include <bits/stdc++.h>
using namespace std;
const long long int N = 1 * 1e2 + 2;
long long int n, k;
long long int a[N];
int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  long long int tt;
  cin >> tt;
  for (long long int qq = 1; qq <= tt; ++qq) {
    cin >> n >> k;
    set<long long int> s;
    for (long long int i = 0; i < n; i++) {
      cin >> a[i];
      s.insert(a[i]);
    }
    if (s.size() > k) {
      cout << -1 << '\n';
      continue;
    }
    for (long long int i = 1; i <= n; ++i) {
      if ((s.size() < k) && (s.find(i) == s.end())) s.insert(i);
    }
    cout << n * (long long int)s.size() << '\n';
    for (long long int i = 1; i <= n; ++i) {
      for (long long int x : s) {
        cout << x << ' ';
      }
    }
    cout << '\n';
  }
  return 0;
}
