#include <bits/stdc++.h>
using namespace std;
const int LIM = 5e5 + 3;
int arr[LIM + 3];
long long inf = 1e18;
int main() {
  int tc;
  cin >> tc;
  while (tc--) {
    set<int> cur;
    int n, k;
    cin >> n >> k;
    bool is = false;
    for (int i = 0; i < n; i++) {
      scanf("%d", &arr[i]);
      cur.insert(arr[i]);
    }
    if (cur.size() > k) {
      puts("-1");
      continue;
    }
    int i = 1;
    while (cur.size() != k) cur.insert(i), i++;
    cout << n * k << endl;
    for (int i = 0; i < n; i++)
      for (auto el : cur) printf("%d ", el);
    cout << endl;
  }
}
