#define _USE_MATH_DEFINES

#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <set>
#include <string>
#include <algorithm>
#include <cmath>
#include <queue>
#include <stack>
#include <numeric>
#include <random>
#include <ctime>
#include <tuple>

using namespace std;
#define int long long
#define double long double
int MOD = 1e18 + 7;
double EPS = 1e-12;

#pragma comment(linker, "/stack:200000000")
#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#pragma GCC target ("avx2")
#pragma GCC optimization ("O3")
#pragma GCC optimization ("unroll-loops")

double logg(double a, double b) {
    return log(b) / log(a);
}

void kill(vector<bool> &tok, int u, vector<int> par)

signed main() {
#ifdef LOCAL
    freopen("in", "r", stdin);
    freopen("out", "w", stdout);
#endif
    int t;
    cin >> t;
    for (int i = 0; i < t; i++) {
        int n, m, a, b;
        cin >> n >> m >> a >> b;
        a--;
        b--;
        vector<vector<int>> g(n);
        for(int j = 0; j < m; j++){
            int u, v;
            cin >> u >> v;
            u--;
            v--;
            g[u].push_back(v);
            g[v].push_back(u);
        }
        queue<int> q;
        vector<int> st;
        q.push(a);
        vector<bool> used(n, 0);
        vector<bool> tok(n, 0);
        while(!q.empty()){
            int u = q.front();
            q.pop();
            used[u] = 1;
            for(auto j : g[u]){
                if(j == b){

                }
            }
        }
    }
}