#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
#define X first
#define Y second
#define SZ(a) ((int)a.size())
#define ALL(v) v.begin(), v.end()
#define pb push_back

vector<int> G[200005], ans;
int sqn, vis[200005];

int dfs(int u) {
    vis[u] = 1;
    int mx = -sqn - 1, mn = sqn + 1;
    int cnt = 0;
    for (int i : G[u])
        if (!vis[i]) {
            int res = dfs(i) + 1;
            mx = max(res, mx);
            mn = min(res, mn);
            ++cnt;
        }
    if (!cnt) mx = 0;
    else { 
        if (-mn >= mx) mx = mn;
        if (mx == sqn) ans.pb(u), mx = -sqn;
    }
    return mx;
}

void solve() {
    int n, m;
    cin >> n >> m;
    ans.clear();
    for (int i = 1; i <= n; ++i)
        G[i].clear(), vis[i] = 0;
    sqn = sqrt(n);
    while (sqn * sqn < n) ++sqn;
    while (m--) {
        int a, b;
        cin >> a >> b;
        G[a].pb(b);
    }
    if (dfs(1) > 0 || n == 1) ans.pb(1);
    cout << SZ(ans) << "\n";
    for (int i = 0; i < SZ(ans); ++i)
        cout << ans[i] << " \n"[i + 1 == SZ(ans)];
}

int main() {
    ios::sync_with_stdio(0), cin.tie(0);
    int t;
    cin >> t;
    while (t--) {
        solve();
    }
}