#include <bits/stdc++.h>
#define F first
#define S second
#define pb push_back

using namespace std;
typedef long long ll;

#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;

#define ordered_set tree<pair<ll,int>, null_type,less<pair<ll,int>>, rb_tree_tag,tree_order_statistics_node_update>

const int INF = 1e8;
const int mxN = 2e5 + 9;
const int mxK = 2e2 + 9;
const int MOD = 1000000007;

vector <int> adj[mxN];

void solve () {
    int n;
    cin >> n;

    int m;
    cin >> m;

    int s, t;
    cin >> s >> t;

    for (int i = 1; i <= m; i++) {
        int u, v;
        cin >> u >> v;

        adj[u].pb (v);
        adj[v].pb (u);
    }

    vector <int> dist (n + 1, INF);
    vector <vector <int>> dp (n + 1, vector <int> (2, 0));

    queue <pair <int, int> > q;
    q.push ({s, 0});

    dist[s] = 0;
    dp[s][0] = 1;

    while (!q.empty ()) {
        auto [v, diff] = q.front();
        q.pop();

        for (auto u: adj[v]) {
            if (diff) {
                if (dist[v] + 1 == dist[u]) {
                    if (dp[v][1] == 0)
                        q.push ({u, 1});

                    dp[u][1] += dp[v][1];
                }
            } else {
                if (dist[v] + 1 < dist[u]) {
                    dist[u] = dist[v] + 1;
                    dp[u][0] += dp[v][0];

                    q.push ({u, 0});
                } else if (dist[v] + 1 == dist[u]) {
                    dp[u][0] += dp[v][0];
                } else if (dist[v] == dist[u]) {
                    dp[u][1] += dp[v][0];

                    q.push ({u, 1});
                }
            }
        }
    }


    //cout << dp[t][0] << ' ' << dp[t][1] << "\n";
    cout << dp[t][0] + dp[t][1] << "\n";

    for (int i = 1; i <= n; i++)
        adj[i].clear();

    return;
}

int main () {
    int t = 1;
    cin >> t;

    //preCalc ();
    while (t--) {
        solve ();
    }

    return 0;
}