#include<bits/stdc++.h>
using namespace std;

typedef long long ll;
const int N=1e6+3;
int n,m,a[N];
vector<int>ve[N];
void Solve()
{
	cin>>n>>m;
	for(int i=1;i<=n;i++)ve[i].clear(),a[i]=0;
	for(int i=1,x,y;i<=m;i++)cin>>x>>y,ve[x].push_back(y);
	for(int i=1;i<=n;i++)for(int x:ve[i])a[x]=max(a[x],(a[i]+1)%3);
	cout<<count(a+1,a+n+1,2)<<endl;
	for(int i=1;i<=n;i++)if(a[i]==2)cout<<i<<" ";
	cout<<endl; 
}
int main()
{
	int T;cin>>T;
	while(T--)Solve();
	return 0; 
}