H

#include<bits/stdc++.h>

#define endl "\n"
using namespace std;
using ll = long long;
using ld = long double;
using pii = pair<int, int>;

constexpr int N = 2e5 + 5;

int t, n, m;

vector<int> start, fin;
vector<int> num;

void Solve() {
  cin >> n >> m;
  num.resize(n + 1);
  for (int i = 0, a, b; i < m; i++) {
    cin >> a >> b;
    if (a > b) {
      start.push_back(b);
      fin.push_back(a);
    }
  }
  sort(start.begin(), start.end());
  sort(fin.begin(), fin.end());
  int cur = 0, si = 0, fi = 0;
  for (int i = 1; i <= n; i++) {
    while(si < m && start[si] == i)
      cur++, si++;
    num[i] = cur;
    while(fi < m && fin[fi] == i)
      cur--, fi++;
  }
  int val = *max_element(num.begin(), num.end());
  if (val != m - n + 2) {
    cout << 0 << endl;
  }
  else {
    vector<int> ans;
    for (int i = 1; i <= n; i++)
      if (num[i] == val)
        ans.push_back(i);
    cout << ans.size() << " ";
    for (int v: ans)
      cout << v  << " ";
    cout << endl;
  }
  start.clear();
  fin.clear();
  num.clear();
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  cin >> t;
  while(t--)
  //auto start = chrono::high_resolution_clock::now();
    Solve();
  //auto end = chrono::high_resolution_clock::now();
  //cout << endl << (chrono::duration_cast<chrono::duration<double>>(end - start)).count();
  return 0;
}