#include <iostream>
#include <vector>
#include <cmath>
#include <map>
#include <string>
#include <set>
#include <algorithm>
#include <queue>
using namespace std;
typedef long long ll;
int main() {

    int t;
    cin >> t;
    while (t--) {
        int n, m, a, b;
        cin >> n >> m >> a >> b;
        vector<vector<int> > v;
        vector<int> vec;
        v.insert(v.begin(),n+10,vec);
        for (int i = 0; i < m; i++) {
            int c,d;
            cin >> c >> d;
            v[c].push_back(d);
            v[d].push_back(c);
        }
        vector<int> vk;
        if (t == 2) {
            int kk = 0;
        }
        int kkk = 0;
        while (1 == 1) {
            kkk++;
            vector<int> dp(n + 10, -1);
            vector<int> vs(n+10,0);
            for (int i = 0; i < vk.size(); i++) {
                vs[vk[i]] = true;
            }

            vs[a]  = true;
            queue<int> qi;
            qi.push(a);
            while (!qi.empty()) {

                int t = qi.front();
                qi.pop();

                for (int i = 0; i < v[t].size(); i++) {
                    if (kkk > 1 && t == a && v[t][i] == b) {
                        continue;
                    }
                    if (vs[v[t][i]] == 0) {
                        dp[v[t][i]] = t;
                        qi.push(v[t][i]);
                        vs[v[t][i]] = true;
                    }
                }
            }
            if (dp[b] == -1) {
               break;
            }
            int k = b;


            while (k != a) {
                k = dp[k];
                vk.push_back(k);
            }
        }
        if (vk.size() == 0) {
            cout<<0<<endl;
            continue;
        }
        vector<int> vis(n+10,0);
        vis[a] = true;
        vis[b] = true;
        for (int i = 0; i < vk.size(); i++) {
            queue<int> qi;
            qi.push(vk[i]);
            while (!qi.empty()) {
                int t = qi.front();
                qi.pop();
                if (vis[t])
                    continue;
                vis[t] = true;
                for (int j = 0; j < v[t].size(); j++) {
                    if (vis[v[t][j]] == 0) {
                        qi.push(v[t][j]);
                    }
                }
            }
        }
        int br1 = 0;
        queue<int> qi;
        while (!qi.empty())
            qi.pop();
        qi.push(a);
        vis[a] = false;
        vis[b] = true;
        while (!qi.empty()) {
            int t = qi.front();
             qi.pop();
             if (vis[t])
                 continue;
             vis[t] = true;
             br1++;
             for (int i = 0; i < v[t].size(); i++) {
                 if (vis[v[t][i]] == 0) {
                     qi.push(v[t][i]);
                 }
             }
        }
        while (!qi.empty())
            qi.pop();
        vis[b] = false;
        vis[a] = true;
        qi.push(b);
        int br2 = 0;
        while (!qi.empty()) {
            int t = qi.front();
            qi.pop();
            if (vis[t])
                continue;
            vis[t] = true;
            br2++;
            for (int i = 0; i < v[t].size(); i++) {
                if (vis[v[t][i]] == 0) {
                    qi.push(v[t][i]);
                }
            }
        }
        br1--;
        br2--;
        ll br = (ll)br1 * (ll)br2;
        cout<<br<<endl;
    }

    return 0;

}