#include<bits/stdc++.h>
using namespace std;
#define endl '\n'
#define FAST cin.tie(0);cout.tie(0);ios::sync_with_stdio(false);
const int N=1e4+10;
struct G
{
	int nxt,to,edge;
}g[N];
int head[N],tot;
inline void add(int a,int b,int c)
{
	g[++tot]=(G){head[a],b,c};
	head[a]=tot;
}
int dist[N],c[N];
bool vis[N];
int n,m;
const int inf=1e9;
queue<int> q;
bool spfa(int s)
{
	fill(dist,dist+N,inf);
	q.push(s);
	dist[s]=0;
	vis[s]=1;
	while(!q.empty())
	{
		int u=q.front();
		q.pop();
		vis[u]=0;
		for(int i=head[u];i;i=g[i].nxt)
		{
			int v=g[i].to;
			if(dist[v]>dist[u]+g[i].edge)
			{
				dist[v]=dist[u]+g[i].edge;
				c[v]=c[u]+1;
				if(c[v]>n)
				{
					return 1;
				}
				if(!vis[v])
				{
					q.push(v);
					vis[v]=1;
				}
			}
		}
	}
}
int main()
{
    FAST;
    int T;
    cin>>T;
    while(T--)
    {
        cin>>n>>m;
        for(int i=1;i<=m;i++)
        {
        	static int a,b,w;
        	cin>>a>>b>>w;
        	add(a,b,w);
    	}
    	if(spfa(1)) cout<<"YES"<<endl;
    	else cout<<"NO"<<endl;
    }
    return 0;
}

spfa判负环，感觉没问题，样例是过的

求调