#include <iostream>

using namespace std;
#define INF 99999999;

double arr[10001][10001];
int visit[10001];
double dist[10001];
int computer, node;

void dijkstra()
{
    int i,j;
    int min;
    int v;
    dist[0] = 1;        
    for ( i =0;i <computer; i++)
    {
        min = INF;
        for ( j =0 ; j <computer; j++)
        {
            if ( visit[j] == 0 && min > dist[j])
            {
                min = dist[j];
                v = j;
            }
        }

        visit[v] = 1;  


        for ( j = 0;j < computer; j++)      
        {
            if ( dist[j] > dist[v] * arr[v][j] && arr[v][j]!=0 )       
        {   
            dist[j] = dist[v] * arr[v][j];
            }
        }

    }
}

int main(){

    int testcase ;

    cin>>testcase;
    int x,y;
    double weight;
    for(int t=0 ;t<testcase;t++){

        cin>>computer>>node;

        for(int i=0; i<computer; i++){
            visit[i]=0;
        }



        for(int i=0; i<computer;i++){

            for(int j=0; j<computer; j++){
                if(i!=j)
                    arr[i][j]= INF;

            }

        }



        for(int i=0; i<node;i++){
            cin>>x>>y;
            scanf("%lf", &weight);
            if(arr[x][y]>weight)
                arr[x][y]= weight;  
        }   



        for ( int i =0;i <computer; i++)
        {
             dist[i] = INF;
        }
        dijkstra();
        printf("%.10lf\n",dist[computer-1]);

    }

     return 0;
}