#include <bits/stdc++.h>
using namespace std;
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long T = 1;
  cin >> T;
  while (T--) {
    long long N, K;
    cin >> N >> K;
    long long A[N];
    long long i, j;
    set<long long> s;
    for (i = 0; i < N; i++) {
      cin >> A[i];
      s.insert(A[i]);
    }
    if (s.size() > K) {
      cout << -1 << "\n";
      continue;
    }
    cout << N * K << "\n";
    for (i = 0; i < N; i++) {
      for (long long b : s) cout << b << " ";
      for (j = 0; j < K - s.size(); j++) cout << 1 << " ";
    }
    cout << "\n";
  }
  return 0;
}
