#include <bits/stdc++.h>

#define all(x) x.begin(), x.end()
#define NL std::cout << '\n'

using lnt = long long;
lnt linf = 1ll << 62;
int inf = 0x3f3f3f3f;

void solve() {
  auto fail = []() {
    std::cout << -1; NL;
  };
  int n, m; std::cin >> n >> m;
  std::vector<lnt> v1(n), v2(m);
  for (auto &x : v1) { std::cin >> x; }
  for (auto &x : v2) { std::cin >> x; }
  std::sort(v1.rbegin(), v1.rend());
  std::sort(v2.rbegin(), v2.rend());
  std::vector<lnt> ret;
  for (int i = 0, j = 0; i < m && j < n; ++i, ++j) {
    if (v1[j] > v2[i]) {
      return fail();
    }
    if (v1[j] == v2[i]) { continue; }
    for (lnt x = v1[j]; x < v2[i]; ++x) {
      ret.emplace_back(x);
    }
  }
  if (ret.size() > n-m) { return fail(); }
  std::priority_queue<lnt, std::vector<lnt>, std::greater<>> q;
  for (int i = m + ret.size(); i < n; ++i) { q.emplace(v1[i]); }
  while (!q.empty()) {
    lnt x = q.top(); q.pop();
    if (x+1 > v2.back()) { return fail(); }
    ret.emplace_back(x);
    q.emplace(x+1); q.pop();
  }
  std::sort(all(ret));
  std::cout << ret.size(); NL;
  for (auto x : ret) {
    std::cout << x << " ";
  } NL;
}

signed main() {
  std::ios::sync_with_stdio(false); std::cin.tie(nullptr);
  int t = 1;
  std::cin >> t;
  while (t--) {
    solve();
  }
  return 0;
}