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