#include <bits/stdc++.h>
using namespace std;
int a[105], b[505], cnt[105];
int main() {
  int T;
  cin >> T;
  while (T--) {
    int n, k;
    cin >> n >> k;
    vector<int> v;
    memset(cnt, 0, sizeof(cnt));
    for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
    int c = 0;
    for (int i = 1; i <= n; i++) cnt[a[i]]++;
    for (int i = 1; i <= n; i++)
      if (cnt[i]) c++, v.push_back(i);
    if (c > k) {
      puts("-1");
      continue;
    }
    printf("%d\n", n * k);
    for (int i = 1; i <= n; i++) {
      for (int j = 0; j < k; j++) printf("%d ", v[j % v.size()]);
    }
    printf("\n");
  }
  return 0;
}
