#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int t;
  cin >> t;
  while (t--) {
    long long int n, k;
    cin >> n >> k;
    set<long long int> s;
    long long int a;
    for (long long int i = 0; i < n; i++) {
      cin >> a;
      s.insert(a);
    }
    if (s.size() > k)
      cout << -1 << endl;
    else {
      cout << n * k << endl;
      for (int i = 0; i < n; i++) {
        for (int i : s) cout << i << " ";
        for (int j = 0; j < k - (s.size()); j++) cout << 1 << " ";
      }
      cout << endl;
    }
  }
}
