#include <bits/stdc++.h>
using namespace std;
int main(int argc, const char* argv[]) {
  int t = 0;
  cin >> t;
  int arr[101];
  for (int i = 0; i < t; ++i) {
    int n, k = 0;
    cin >> n >> k;
    for (int j = 0; j < n; ++j) {
      cin >> arr[j];
    }
    vector<int> nums(arr, arr + n);
    sort(nums.begin(), nums.end());
    nums.erase(unique(nums.begin(), nums.end()), nums.end());
    if (nums.size() > k) {
      cout << "-1" << endl;
      continue;
    }
    while (nums.size() < k) {
      nums.emplace_back(1);
    }
    vector<int> result;
    int curr = 0;
    int index = 0;
    while (curr < n) {
      result.emplace_back(nums[index++ % nums.size()]);
      if (result.back() == arr[curr]) {
        ++curr;
      }
    }
    cout << result.size() << endl;
    for (int item : result) {
      cout << item << " ";
    }
    cout << endl;
  }
  return 0;
}
