#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  while (t--) {
    int n, k;
    cin >> n >> k;
    int a[n], b[101] = {};
    for (int i = 0; i < n; i++) {
      cin >> a[i];
      b[a[i]]++;
    }
    std::vector<int> c;
    for (int i = 0; i < 101; i++) {
      if (b[i] != 0) {
        c.push_back(i);
      }
    }
    if (c.size() > k) {
      cout << -1 << "\n";
      continue;
    } else if (c.size() < k) {
      int x = k - c.size();
      for (int i = 1; i < 101 && x; i++) {
        if (b[i] == 0) {
          c.push_back(i);
          x--;
        }
      }
    }
    cout << (n * c.size()) << "\n";
    while (n--) {
      for (int i = 0; i < c.size(); i++) {
        cout << c[i] << " ";
      }
    }
    cout << "\n";
  }
  return 0;
}
