#include <bits/stdc++.h>
using namespace std;
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  long long ct;
  cin >> ct;
  while (ct--) {
    long long n, k;
    cin >> n >> k;
    vector<long long> a(n), was(n + 1), s;
    long long tmp = 0;
    for (long long i = 0; i < (n); ++i) {
      cin >> a[i];
      if (!was[a[i]]) {
        tmp++;
        was[a[i]]++;
      }
    }
    if (tmp > k) {
      cout << "-1\n";
    } else {
      for (long long i = 1; i < (n + 1); ++i) {
        if (tmp < k and !was[i]) {
          s.push_back(i);
          tmp++;
        }
        if (was[i]) s.push_back(i);
      }
      cout << n * s.size() << "\n";
      for (long long i = 0; i < (n); ++i) {
        for (long long j = 0; j < (s.size()); ++j) {
          cout << s[j] << " ";
        }
      }
      cout << "\n";
    }
  }
}
