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