#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long T;
  cin >> T;
  while (T--) {
    long long n, k, i, j, x;
    vector<long long> v, v2;
    cin >> n >> k;
    for (i = 0; i < n; ++i) {
      long long xx;
      cin >> xx;
      v.push_back(xx);
    }
    v2 = v;
    sort(v2.begin(), v2.end());
    (v2).resize(unique(v2.begin(), v2.end()) - (v2).begin());
    if (v2.size() > k) {
      cout << -1 << "\n";
      continue;
    }
    cout << 10000 << "\n";
    v.clear();
    int xx = (int)v2.size();
    for (i = 0; i < k; i++) v.push_back(v2[i % xx]);
    for (i = 0; i < 10000; i++) {
      cout << v[(i % k)] << " ";
    }
    cout << "\n";
  }
  return 0;
}
