#include <bits/stdc++.h>
using namespace std;
int main(int argc, char** argv) {
  int t, n, k, a;
  bool visit[105];
  cin >> t;
  while (t--) {
    cin >> n >> k;
    memset(visit, 0, sizeof(visit));
    vector<int> v;
    for (int i = 0; i < n; i++) {
      cin >> a;
      if (!visit[a]) {
        visit[a] = 1;
        v.push_back(a);
      }
    }
    if (k < v.size())
      cout << -1 << '\n';
    else {
      k -= v.size();
      for (int i = 1; i <= n && k; i++) {
        if (!visit[i]) {
          v.push_back(i);
          k--;
        }
      }
      int vs = v.size();
      cout << n * vs << '\n';
      for (int i = 0; i < n; i++) {
        for (int j = 0; j < vs; j++) cout << v[j] << ' ';
      }
      cout << '\n';
    }
  }
  return 0;
}
