#include <bits/stdc++.h>
using namespace std;
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  ;
  long long t;
  cin >> t;
  for (long long q = 0; q < t; q++) {
    long long n, k;
    cin >> n >> k;
    long long a[n], b[n + 1], x = 0;
    for (long long i = 0; i < n; i++) {
      cin >> a[i];
      b[i + 1] = 0;
    }
    for (long long i = 0; i < n; i++) b[a[i]] = 1;
    for (long long i = 1; i <= n; i++) x += b[i];
    if (x > k)
      cout << "-1"
           << "\n";
    else {
      cout << n * k << "\n";
      for (long long i = 0; i < n; i++) {
        long long y = k - x;
        for (long long j = 1; j <= n; j++) {
          if (b[j]) cout << j << " ";
        }
        for (long long j = 1; j <= n; j++) {
          if (!b[j] && y) {
            cout << j << " ";
            --y;
          }
        }
      }
      cout << "\n";
    }
  }
  return 0;
}
