#include<bits/stdc++.h>
using namespace std;
int n, m;
vector<int> a[100004];
vector<int> b[100004];
stack<int> x;
int ans;
bool used[10005];
void begin(){
cin >> n >> m;
for(int i = 1; i <= m ; i++){
int x, y;
cin >> x >> y;
a[x].push_back(y);
b[y].push_back(x);
}
ans = 0;
}
void dfs1(int u){
used[u] = true;
for(int v : a[u]){
if(!used[v]){
dfs1(v);
}
}
x.push(u);
}
void dfs2(int u){
used[u] = true;
for(int v : b[u]){
if(!used[v]){
dfs2(v);
}
}
}
void solve(){
memset(used, false, sizeof(used));
for(int i = 1; i <= n; i++){
if(!used[i]){
dfs1(i);
}
}
memset(used, false, sizeof(used));
while(!x.empty()){
int top = x.top();
x.pop();
if(!used[top]){
dfs2(top);
ans++;
}
}
if(ans == 1) cout << "YES";
else cout << "NO";
}
int main(){
int t;
cin >> t;
while(t--){
begin();
solve();
cout << endl;
}
}
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