#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  while (t--) {
    int n, k;
    cin >> n >> k;
    int a[n], x;
    set<int> distinct;
    for (int i = 0; i < n; i++) {
      cin >> a[i];
      distinct.insert(a[i]);
    }
    if (distinct.size() > k)
      cout << "-1 \n";
    else {
      cout << n * k << "\n";
      for (int i = 0; i < n; i++) {
        for (auto x : distinct) cout << x << " ";
        for (int i = 0; i < k - distinct.size(); i++) cout << "1 ";
      }
      cout << "\n";
    }
  }
  return 0;
}
