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