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