#include <bits/stdc++.h>
using namespace std;
int main() {
  long long t;
  cin >> t;
  while (t--) {
    long long n, k;
    cin >> n >> k;
    set<long long> s;
    set<long long>::iterator it;
    long long a[n];
    for (long long i = 0; i < n; i++) {
      cin >> a[i];
      s.insert(a[i]);
    }
    if (s.size() > k) {
      cout << "-1\n";
      continue;
    }
    vector<long long> v;
    for (it = s.begin(); it != s.end(); it++) {
      v.push_back(*it);
    }
    cout << n * k << endl;
    for (long long i = 0; i < n; i++) {
      for (long long j = 0; j < v.size(); j++) {
        cout << v[j] << " ";
      }
      if (k > s.size()) {
        int x = k - s.size();
        for (long long j = 0; j < x; j++) {
          cout << "1 ";
        }
      }
    }
    cout << endl;
  }
  return 0;
}
