wa#12!

#include<bits/stdc++.h>
using namespace std;
const int N=1e6;
int n,m;
int dist[N];
int vis[N];
int cnt[N];
struct node{
	int to;
	int w;
};
vector<node> g[N];
bool spfa(){
	memset(dist,0,sizeof dist);
	memset(cnt,0,sizeof cnt);
	queue<int>q;
	for(int i=1;i<=n;i++){
		q.push(i);
		vis[i]=1;
	}
	while(q.size()){
		int x=q.front();q.pop();
		vis[x]=0;
		for(int i=0;i<g[x].size();i++){
			int y=g[x][i].to,z=g[x][i].w;
			if(dist[y]>dist[x]+z){
				dist[y]=dist[x]+z;
				cnt[y]=cnt[x]+1;
				if(!vis[y]){
					q.push(y);
					vis[y]=1;
				}
				if(cnt[y]>n-1)return 1;
			}
		}
	}
	return 0;
}
int main(){
	int t;
	cin>>t;
	while(t--){
		cin>>n>>m;
		for(int i=1;i<=n;i++)g[i].clear();
		for(int i=1;i<=m;i++){
			int a,b,c;
			cin>>a>>b>>c;
			g[a].push_back({b,c});
			if(c>=0) g[b].push_back({a,c});
		}
		if(!spfa())cout<<"NO\n";
		else cout<<"YES\n";
	}
}