wormholes

import sys
import os
if not os.environ.get("ONLINE_JUDGE"):
    sys.stdin = open('./in.txt', 'r')
    sys.stdout = open('./out.txt', 'w')

inf = sys.maxsize


def bellmanford(el, s, n):
    dist = [inf for _ in range(n)]

    dist[s] = 0
    for i in range(n-1):
        for edge in el:
            # print(edge)
            u, v, w = edge

            if dist[v] > dist[u]+w:
                dist[v] = dist[u] + w

    for edge in el:
        u, v, w = edge
        if dist[v] > dist[u]+w:
            return True

    return False


for _ in range(int(input())):
    n, m = map(int, input().split())
    el = []
    for _ in range(m):
        u, v, w = map(int, input().split())
        el.append([u, v, w])

    if bellmanford(el, 0, n):
        print("possible")
    else:
        print("not possible")