#include <bits/stdc++.h>
using namespace std;
void init() {}
long long power(long long x, unsigned long long y) {
  long long res = 1;
  while (y > 0) {
    if (y & 1) res = res * x;
    y = y >> 1;
    x = x * x;
  }
  return res;
}
long long gcd(long long a, long long b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  init();
  long long t;
  cin >> t;
  while (t--) {
    long long n, k;
    cin >> n >> k;
    set<long long> s;
    vector<long long> a(n);
    for (long long &i : a) {
      cin >> i;
      s.insert(i);
    }
    if (s.size() > k) {
      cout << "-1" << '\n';
      continue;
    }
    cout << n * k << endl;
    for (long long i = 0; i < n; i++) {
      for (long long x : s) cout << x << " ";
      for (long long j = 0; j < k - s.size(); j++) cout << '1' << " ";
    }
    cout << endl;
  }
}
