#include <bits/stdc++.h>
using namespace std;
int a[105];
int b[105];
map<int, int> mm;
int main(int argc, const char* argv[]) {
  int t, n, k;
  cin >> t;
  while (t--) {
    cin >> n >> k;
    mm.clear();
    int cnt = 0;
    int ans = 0;
    for (int i = 1; i <= n; i++) {
      cin >> a[i];
      if (!mm[a[i]]) {
        cnt++;
        mm[a[i]] = 1;
        b[ans++] = a[i];
      }
    }
    if (cnt > k) {
      cout << -1 << endl;
      continue;
    }
    for (int i = 1; i <= n; i++) {
      if (!mm[i]) {
        b[ans++] = i;
      }
    }
    cout << n * k << endl;
    for (int i = 0; i < n; i++) {
      for (int j = 0; j < k; j++) {
        cout << b[j] << " ";
      }
    }
    cout << endl;
  }
  return 0;
}
