#include <bits/stdc++.h>
using namespace std;
const int inf = 0x3f3f3f3f, mod = 1e9 + 7;
typedef queue<int> qint;
typedef valarray<int> va;
typedef set<int> sint;
typedef stack<int> stint;
typedef map<int, int> dicti;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  ;
  int n, k, a;
  int t;
  cin >> t;
  while (t--) {
    cin >> n >> k;
    set<int> s;
    for (int i = 0; i < (int)(n); ++i) {
      cin >> a;
      s.insert(a);
    }
    if (s.size() > k) {
      cout << "-1\n";
      continue;
    }
    int l = s.size();
    cout << n * k << endl;
    for (int i = 0; i < (int)(n); ++i) {
      for (int b : s) cout << b << ' ';
      for (int j = 0; j < (int)(k - l); ++j) cout << "1 ";
    }
    cout << endl;
  }
  return 0;
}
