#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int t;
  cin >> t;
  while (t--) {
    int n, k;
    cin >> n >> k;
    int arr[n + 5];
    set<int> s;
    for (int i = 1; i <= n; i++) {
      cin >> arr[i];
      s.insert(arr[i]);
    }
    int d = s.size();
    if (d > k) {
      cout << "-1\n";
      continue;
    } else {
      for (int i = 1; i <= 100; i++) {
        if (d == k) {
          break;
        }
        s.insert(i);
        d = s.size();
      }
      cout << n * k << "\n";
      for (int i = 1; i <= n; i++) {
        for (auto it = s.begin(); it != s.end(); it++) {
          cout << *it << " ";
        }
      }
      cout << "\n";
    }
  }
  return 0;
}
