#include <bits/stdc++.h>
using namespace std;
template <typename A, typename B>
string to_string(pair<A, B> p);
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);
string to_string(const string& s) { return '"' + s + '"'; }
string to_string(const char* s) { return to_string((string)s); }
string to_string(bool b) { return (b ? "true" : "false"); }
string to_string(vector<bool> v) {
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (i) res += ", ";
    res += to_string(v[i]);
  }
  res += "}";
  return res;
}
template <size_t N>
string to_string(bitset<N> v) {
  string res = "";
  for (size_t i = 0; i < N; i++) {
    res += static_cast<char>('0' + v[i]);
  }
  return res;
}
template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto& x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}
template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " +
         to_string(get<2>(p)) + ")";
}
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " +
         to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}
void debug_out() { cerr << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}
mt19937 gen(time(0));
void solve() {
  long long n, m;
  cin >> n >> m;
  set<long long> g[n], g2[n];
  for (long long i = 0; i < m; i++) {
    long long x, y;
    cin >> x >> y;
    x--;
    y--;
    g[x].insert(y);
    g2[y].insert(x);
  }
  auto F = [&](long long x) {
    for (auto y : g[x]) {
      g2[y].erase(x);
    }
    for (auto y : g2[x]) {
      g[y].erase(x);
    }
    g[x].clear();
    g2[x].clear();
  };
  set<long long> ans;
  for (long long i = 0; i < n; i++) {
    while (g[i].size() > 0) {
      long long v = *g[i].begin();
      g[i].erase(v);
      if (g[v].size() == 0) continue;
      if (g[v].size() == 1) {
        long long x = *g[v].begin();
        F(x);
        ans.insert(x);
        continue;
      }
      long long x = *g[v].begin(), y = *g[v].rbegin();
      long long res = g[x].size() * ((long long)g2[x].size() - 1);
      long long res2 = g[y].size() * ((long long)g2[y].size() - 1);
      if (res + res2 <= 1 || (res + res2 == 2 && gen() % 3 == 0)) {
        F(v);
        ans.insert(v);
        continue;
      }
      F(x), F(y);
      ans.insert(x);
      ans.insert(y);
    }
  }
  cout << ans.size() << endl;
  for (auto x : ans) cout << x + 1 << " ";
  cout << endl;
}
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long q;
  cin >> q;
  while (q--) {
    solve();
  }
}
