#include <bits/stdc++.h>
using namespace std;
using namespace std::chrono;
template <typename A>
ostream &operator<<(ostream &cout, vector<A> const &v);
template <typename A, typename B>
ostream &operator<<(ostream &cout, pair<A, B> const &p) {
  return cout << "(" << p.first << ", " << p.second << ")";
}
template <typename A>
ostream &operator<<(ostream &cout, vector<A> const &v) {
  cout << "[";
  for (int i = 0; i < v.size(); i++) {
    if (i) cout << ", ";
    cout << v[i];
  }
  return cout << "]";
}
template <typename A, typename B>
istream &operator>>(istream &cin, pair<A, B> &p) {
  cin >> p.first;
  return cin >> p.second;
}
mt19937 rng(61378913);
void usaco(string filename) {
  freopen((filename + ".in").c_str(), "r", stdin);
  freopen((filename + ".out").c_str(), "w", stdout);
}
const long double pi = 3.14159265358979323846;
long long n, m, k, q, l, r, x, y, z;
long long a[1000005];
long long b[1000005];
long long c[1000005];
string second, t;
long long ans = 0;
void solve(int tc) {
  cin >> n >> m;
  vector<int> edges[n];
  long long id[n];
  long long real_id[n];
  long long stid[n];
  memset(stid, 0, sizeof(stid));
  memset(real_id, 0, sizeof(real_id));
  memset(id, 0, sizeof(id));
  for (long long i = 0; i < (m); ++i) {
    cin >> x >> y;
    --x;
    --y;
    edges[x].push_back(y);
    ++id[y];
    ++real_id[y];
    ++stid[y];
  }
  bool on[n];
  memset(on, 0, sizeof(on));
  bool vis[n];
  memset(vis, 0, sizeof(vis));
  queue<int> q;
  for (long long i = 0; i < (n); ++i)
    if (id[i] == 0) q.push(i);
  while (!q.empty()) {
    int x = q.front();
    q.pop();
    if (vis[x]) continue;
    vis[x] = 1;
    if (((long long)edges[x].size()) == 0 || id[x] == 0) on[x] = 1;
    for (int y : edges[x]) {
      if (!on[x]) --id[y];
      --real_id[y];
      if (real_id[y] == 0) q.push(y);
    }
  }
  long long c = 0;
  for (long long i = 0; i < (n); ++i)
    if (!on[i]) ++c;
  if (c <= 4 * n / 7) {
    cout << c << '\n';
    for (long long i = 0; i < (n); ++i)
      if (!on[i]) cout << i + 1 << " ";
    cout << '\n';
    return;
  }
  for (long long i = 0; i < (n); ++i) real_id[i] = stid[i];
  memset(on, 0, sizeof(on));
  memset(vis, 0, sizeof(vis));
  long long dep[n];
  memset(dep, 0, sizeof(dep));
  q = queue<int>();
  for (long long i = 0; i < (n); ++i)
    if (real_id[i] == 0) {
      q.push(i);
      dep[i] = 0;
    }
  while (!q.empty()) {
    int x = q.front();
    q.pop();
    if (vis[x]) continue;
    vis[x] = 1;
    if (dep[x] > 1) {
      on[x] = 1;
      dep[x] = -1;
    }
    for (int y : edges[x]) {
      --real_id[y];
      dep[y] = max(dep[y], dep[x] + 1);
      if (real_id[y] == 0) q.push(y);
    }
  }
  c = 0;
  for (long long i = 0; i < (n); ++i)
    if (on[i]) ++c;
  if (c <= 4 * n / 7) {
    cout << c << '\n';
    for (long long i = 0; i < (n); ++i)
      if (on[i]) cout << i + 1 << " ";
    cout << '\n';
  } else {
    cout << n - c << '\n';
    for (long long i = 0; i < (n); ++i)
      if (!on[i]) cout << i + 1 << " ";
    cout << '\n';
  }
}
int main() {
  { ios_base::sync_with_stdio(false); }
  {
    cin.tie(NULL);
    cout.tie(NULL);
  }
  int tc = 1;
  cin >> tc;
  for (int t = 0; t < tc; t++) solve(t);
}
