#include <iostream>
#include <iomanip>
#include <vector>
#include <queue>

using namespace std;

#define REP(i,n) for(int i=0; i<n; ++i)
#define INF 987654321

int N, M;

long double calcNoise(int src, vector<vector<pair<int,long double> > >& graph)
{
    vector<long double> dist(N, INF);
    dist[src] = 1.0;

    priority_queue<pair<long double,int>, vector<pair<long double,int> >, greater<pair<long double,int> > > pq;

    pq.push(make_pair(1.0, src));

    while(!pq.empty())
    {
        long double cost = pq.top().first;
        int here = pq.top().second;
        pq.pop();

        if(dist[here] < cost) continue;

        int size = graph[here].size();      
        REP(i,size)
        {
            int there = graph[here][i].first;
            long double nextCost = cost * graph[here][i].second;

            if(dist[there] > nextCost)
            {
                dist[there] = nextCost;
                pq.push(make_pair(nextCost,there));
            }
        }
    }

    return dist[N-1];
}

int main(void)
{
    int t;
    cin >> t;
    cout << fixed << setprecision(10);
    while(t--)
    {
        cin >> N >> M;

        vector<vector<pair<int,long double> > > graph(N);

        int a, b;
        long double c;

        REP(i,M)
        {
            cin >> a >> b >> c;
            graph[a].push_back(make_pair(b,c));
        }

        cout << calcNoise(0, graph) << endl;
    }
}