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