#include <bits/stdc++.h>
int main(int argc, const char *argv[]) {
  size_t t;
  std::cin >> t;
  while (t--) {
    size_t n, k;
    std::cin >> n >> k;
    std::vector<size_t> a(n);
    for (auto &elem : a) std::cin >> elem;
    std::unordered_set<size_t> elems;
    for (auto elem : a) elems.insert(elem);
    if (elems.size() > k) {
      std::cout << -1 << '\n';
      continue;
    }
    while (elems.size() < k) {
      for (size_t i = 1; i <= n; ++i)
        if (elems.find(i) == elems.end() && elems.size() < k) elems.insert(i);
    }
    std::cout << n * k << '\n';
    for (size_t i = 0; i < n; ++i) {
      for (auto elem : elems) std::cout << elem << ' ';
    }
    std::cout << '\n';
  }
  return 0;
}
