#include <cstring>
#include <iostream>
#include <algorithm>
#include <queue>
#include <bits/stdc++.h>
using namespace std;

const int N = 2010, M = 10010;

int T, n, m;
int h[N], w[M], e[M], ne[M], idx;
int dist[N], cnt[N]; 
bool st[N]; 

void add(int a, int b, int c)
{
    e[idx] = b, w[idx] = c, ne[idx] = h[a], h[a] = idx ++ ;
}

bool spfa()
{
    memset(cnt,0,sizeof cnt);
    memset(dist,0,sizeof dist);
    queue<int> q;

    q.push(1);
    st[1]=true;

    while (q.size()) 
    {
        int t = q.front();
        q.pop();

        st[t] = false;

        for (int i = h[t]; i != -1; i = ne[i])
        {
            int j = e[i];
            if (dist[j] > dist[t] + w[i])
            {
                dist[j] = dist[t] + w[i];
                cnt[j] = cnt[t] + 1;

                if (cnt[j] >= n) return true; 
                
                if (!st[j])
                {
                    q.push(j);
                    st[j] = true;
                }
            }
        }
    }

    return false;
}

int main()
{
    scanf("%d%d",&T);
    while(T--){
        scanf("%d%d", &n, &m);
        idx = 0;
        memset(h, -1, sizeof h);
    
        while (m -- )
        {
            int a, b, c;
            scanf("%d%d%d", &a, &b, &c);
            if(c >= 0) add(b, a, c);
            add(a, b, c);
        }
    
        if (spfa()) puts("YES");
        else puts("NO");
    }
    return 0;
}