#include <iostream>
#include <vector>
#include <iomanip>
#include <queue>
using namespace std;
double solve(int N, int M, int K, int H, vector<int> x, vector<int>y, vector<int> c, vector<int> arr){
priority_queue<pair<double,int>,vector<pair<double,int>>,greater<pair<double,int>>> pq; // {val,node}
vector<vector<pair<int,double>>> graph(N);
for (int i = 0;i<M;i++){
graph[x[i]].push_back({y[i],c[i]});
graph[y[i]].push_back({x[i],c[i]});
}
pq.push({0.0,0});
vector<double> ans(N,1e18);ans[0]=0;
vector<int> visited(N,0);
while(!pq.empty()){
int node = pq.top().second;
pq.pop();
if (visited[node]){continue;}
visited[node]=1;
for (pair<int,double> next:graph[node]){
if (ans[node]+next.second<ans[next.first]){
ans[next.first]=next.second+ans[node];
pq.push({ans[next.first],next.first});
}
}
}
if (ans[H]>=1e18){return -1;}
return ans[H];
}
int main(){
int t;cin >> t;
while(t--){
int n,m,k,h;cin >> n >> m >> k >> h;
vector<int> arr(n);
vector<int> x(m);
vector<int> y(m);
vector<int> c(m);
for (int i = 0;i<n;i++){cin >> arr[i];}
for (int i = 0;i<m;i++){
cin >> x[i] >> y[i] >> c[i];
}
cout << fixed << setprecision(12) << solve(n,m,k,h,x,y,c,arr) << "\n";
}
}
