#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
typedef unsigned long long ULL;
typedef long double LD;
const int INF = 2147483647;
const int S = 1e5+5;
int n,m,tot;
int head[S],ver[S],edge[S],Next[S],dis[S],vis[S],v[S];
inline void add(int x,int y,int z)
{ver[++tot] = y,edge[tot] = z,Next[tot] = head[x],head[x] = tot;}
inline void spfA(int s)
{
	memset(dis,0x7f,sizeof(dis));
	memset(vis,0,sizeof(vis));
	memset(v,0,sizeof(v));
	queue <int> q;
	while(!q.empty()) q.pop();
	dis[s] = 0; 
	vis[s] = 1;
	q.push(s);
	while(!q.empty())
	{
		int x = q.front();
		q.pop();
		vis[x] = 0;
		for(int i = head[x];i;i = Next[i])
		{
			int y = ver[i],z = edge[i];
			if(dis[y] > dis[x]+z)
			{
				dis[y] = dis[x]+z;
				if(!vis[y])
				{
					q.push(y);vis[y] = 1;
					if(++v[x] >= n) {puts("YES");return;}
				}
			}
		}
	}
	puts("NO");
}
inline LL read()
{
	LL x=0,f=1;
	char ch = getchar();
	while(!isdigit(ch)) {if(ch == '-') f = -1;ch = getchar();}
	while(isdigit(ch)) {x=x*10+ch-48;ch=getchar();}
	return f*x;
}
int main(int argc,char *argv[])
{ 
	//freopen("data.in","r",stdin);
	//freopen("data.out","w",stdout);	
	int T = read();
	while(T--)
	{
		int flag = 0;
		n = read(),m = read();
		while(m--)
		{
			int u = read(),v = read(),w = read();
			if(w >= 0) add(u,v,w),add(v,u,w);
			else add(u,v,w);
		}
		spfA(1);
	}
	//printf("Tide used = %.0lf.ds\n",((double)clock()/(double)CLOCKS_PER_SEC) * 1000.0);
	return 0;
}