#include <bits/stdc++.h>

/* run this program using the console pauser or add your own getch, system("pause") or input loop */
using namespace std; 
const int N = 3010;
int u,m,dis[N],cnt,sum[N],T,n,head[N],vis[N];
struct qedge{
	int to,next,quan;
}edge[N * 2];
void add(int x,int y,int z){
	edge[++cnt].to = y;
	edge[cnt].quan = z;
	edge[cnt].next = head[x];
	head[x] = cnt;
}
void spfa(){
	memset(vis,0,sizeof vis);
	memset(head,-1,sizeof head);
	memset(dis,10000,sizeof dis);
	memset(sum,0,sizeof sum); 
	queue<int> q;
	vis[1] = 1;
	dis[1] = 0;
	q.push(1);
	sum[1]++;
	while(!q.empty()){
		u = q.front();
		vis[u] = 0;
		q.pop();
		for(int i = head[u];i;i = edge[i].next){
			int v = edge[i].to;
			if(dis[v] > dis[u] + edge[i].quan){
				dis[v] = dis[u] + edge[i].quan;
				if(!vis[v]){
					vis[v] = 1;
					q.push(v);
					sum[v]++;
					if(sum[v] > n){
						cout<<"YES"<<endl;
						return ;
					}
				}
			}
		}
	}
	cout<<"NO"<<endl;
}
int main(int argc, char** argv) {
	cin>>T;
	while(T--){
		memset(edge,0,sizeof edge);
		cin>>n>>m;
		for(int i = 1;i <= m;i++){
			int a,b,w;
			cin>>a>>b>>w;
			if(w >= 0) add(a,b,w),add(b,a,w);
			else add(a,b,w);
		}	
		spfa();
		cnt = 0;
	}
	return 0;
}