暴力求SG函数即可，记忆化贼方便
/*program from Wolfycz*/
#include<cmath>
#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#define inf 0x7f7f7f7f
using namespace std;
typedef long long ll;
typedef unsigned int ui;
typedef unsigned long long ull;
inline int read(){
int x=0,f=1;char ch=getchar();
for (;ch<'0'||ch>'9';ch=getchar()) if (ch=='-') f=-1;
for (;ch>='0'&&ch<='9';ch=getchar()) x=(x<<1)+(x<<3)+ch-'0';
return x*f;
}
inline void print(int x){
if (x>=10) print(x/10);
putchar(x%10+'0');
}
const int N=1e4,M=1e5;
int pre[M+10],now[N+10],child[M+10],tot;
int can[N+10];
int n,m;
void join(int x,int y){pre[++tot]=now[x],now[x]=tot,child[tot]=y;}
void dfs(int x){
if (can[x]!=-1) return;
bool flag=0;
for (int p=now[x],son=child[p];p;p=pre[p],son=child[p]){
dfs(son);
if (!can[son]) flag=1;
}
can[x]=flag;
}
void init(){
tot=0;
memset(now,0,sizeof(now));
memset(can,-1,sizeof(can));
}
int main(){
for (int Data=read();Data;Data--){
init();
n=read(),m=read(),can[n]=0;
for (int i=1;i<=m;i++){
int x=read(),y=read();
join(x,y);
}
dfs(1);
printf(can[1]?"yes":"no");
putchar('
');
}
return 0;
}