#include <bits/stdc++.h>
using namespace std;
bool kt[101];
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t;
  cin >> t;
  while (t--) {
    int n, k;
    cin >> n >> k;
    set<int> diff;
    for (int i = 0; i < n; ++i) {
      int x;
      cin >> x;
      diff.insert(x);
    }
    if (diff.size() > k)
      cout << "-1\n";
    else {
      cout << n * k << '\n';
      for (int i = 0; i < n; ++i) {
        for (auto& x : diff) cout << x << ' ';
        for (int j = diff.size(); j < k; ++j) cout << 1 << ' ';
      }
      cout << '\n';
    }
  }
  return 0;
}
