#include <stdio.h>
#include <vector>
#include <algorithm>
#include <bits/stdc++.h>
using namespace std;


typedef struct node
{
    int id;
    int weight;
    vector< pair<int, int> > neighbours;
    bool visited;
} Node;
Node graph[1001];
void BellmanFord();
int n_cases;
int n_star_systems;
int n_wormholes;
int dist[1001];
int main()
{
    scanf("%d", &n_cases);
    while(n_cases--){
        scanf("%d %d", &n_star_systems, &n_wormholes);
        for(int i=0; i<n_wormholes; i++){
            int src_system, dest_system, weight;
            scanf("%d %d %d", &src_system, &dest_system, &weight);
            graph[src_system].id = src_system;
            graph[src_system].weight = INT_MAX;
            pair<int, int> p;
            p = make_pair(dest_system,weight);
            graph[src_system].neighbours.push_back(p);

        }
        graph[0].weight = 0;
        BellmanFord();
    }
    return 0;
}
void BellmanFord(){
    for(int i =0; i<n_star_systems-1;i++){
        for(int j = 0; j<(int)graph[i].neighbours.size(); j++){
            //int u = graph[i].id;
            int v = graph[i].neighbours[j].first;
            if(graph[i].weight != INT_MAX && graph[i].weight + graph[i].neighbours[j].second < graph[v].weight){
                graph[v].weight = graph[i].weight +  graph[i].neighbours[j].second;
            }
        }
    }

     for(int i =0; i<n_star_systems-1;i++){
        for(int j = 0; j<(int)graph[i].neighbours.size(); j++){
           // int u = graph[i].id;
            int v = graph[i].neighbours[j].first;
            if(graph[i].weight != INT_MAX && graph[i].weight + graph[i].neighbours[j].second < graph[v].weight){
                printf("not possible\n");
                return;
            }
        }
    }
    printf("possible\n");



}