#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <queue>
using namespace std;
const int N = 2e3 + 10, M = 6e3 + 10;
int ne[M], e[M], h[N], w[M], idx;
int dis[N], cnt[N];
bool st[N];
int n, m;
void add(int a, int b, int c)
{
    e[idx] = b, ne[idx] = h[a], w[idx] = c, h[a] = idx++;
}
bool spfa()
{
    memset(dis, 0x3f, sizeof dis);
    memset(st, 0, sizeof st);
    memset(cnt, 0, sizeof cnt);
    queue<int> q;
    q.push(1);
    dis[1] = 0;
    st[1] = true;
    while (q.size())
    {
        int t = q.front();
        q.pop();
        st[t] = false;

        for (int i = h[t]; ~i; i = ne[i])
        {
            int j = e[i];
            if (dis[j] > dis[t] + w[i])
            {
                dis[j] = dis[t] + w[i];
                if (++cnt[t] >= n)
                    return false;
                if (!st[j])
                {
                    st[j] = true;
                    q.push(j);
                }
            }
        }
    }
    return true;
}
int main()
{
    int T;
    cin >> T;
    while (T--)
    {
        cin >> n >> m;
        memset(h, -1, sizeof h);
        idx = 0;
        for (int i = 0; i < m; i++)
        {
            int a, b, c;
            scanf("%d%d%d", &a, &b, &c);
            if (c >= 0)
                add(a, b, c), add(b, a, c);
            else
                add(a, b, c);
        }
        if (spfa())
            cout << "NO" << endl;
        else
            cout << "YES" << endl;
    }
}

1
3 5
1 2 -8
1 2 -7
1 2 -6
1 2 -5
2 3 4

输出YES，正解NO