#include<bits/stdc++.h>


using namespace std;
const int maxn = 2e5 + 3;
vector<vector<int> > g;
int tin[maxn], fup[maxn];
bool used[maxn];
int timer = 1;
int a, b;
bool fl1 = 0, fl2 = 0;
void cpt(int v){
    if (v == a) fl1 = 1;
    if (v == b) fl2 = 1;
}
void dfs (int v, int p) {
  used[v] = 1;
  tin[v] = fup[v] = timer++;
  int children = 0;
  for (int i = 0; i< g[v].size(); i++) {
    int to = g[v][i];
    if (to == p) continue;
    if (used[to]){
      fup[v] = min(fup[v], tin[to]);
    }else{
      dfs(to, v);
      fup[v] = min(fup[v], fup[to]);
      if (fup[to] >= tin[v] && p != -1)
        cpt(v);
      children++;
    }
  }
  if (p == -1 && children > 1)
    cpt(v);
}
int dp[maxn];
int goa(int v, int p){
    used[v] = 1;
    dp[v] = 1;
    for (int i = 0; i < g[v].size(); i++){
        int to = g[v][i];
        if (to == a){
            if (v != b) return 0;
            continue;
        }
             if (!used[to]){
            int ce = goa(to, v);
            if (v != b && ce == 0) return 0;
            dp[v] += ce;
            }
    }
    return dp[v];
}
int gob(int v, int p){
    used[v] = 1;
    dp[v] = 1;
    for (int i = 0; i < g[v].size(); i++){
        int to = g[v][i];
        if (to == b){
            if (v != a) return 0;
            continue;
        }
            if (!used[to]){
            int ce = gob(to, v);
            if (v != a && ce == 0) return 0;
            dp[v] += ce;
            }
    }
    return dp[v];
}
void solve(){
    int n, m;
    cin >> n >> m >> a >> b;
    a--, b--;
    g.resize(n);
    for (int i = 0; i < m; i++){
        int v, u;
        cin >> v >> u;
        v--, u--;
        g[v].push_back(u);
        g[u].push_back(v);
    }
    dfs(0, -1);
    if (!fl1 || !fl2){cout << 0 << '\n';
        for(int i = 0; i < n; i++){
            tin[i] = fup[i] = dp[i] = used[i] = 0;
        }
        fl1 = 0, fl2 = 0;
        g.clear();
        return;
    }
    for (int i = 0; i < maxn; i++) used[i] = 0;
    goa(b, -1);
    for (int i = 0; i < maxn; i++) used[i] = 0;
    gob(a, -1);
  //  for (int i = 0; i < n; i++) cout << dp[i] << ' '; cout << endl;
    //cout << a << ' ' << dp[a] << ' ' << b << ' ' << dp[b] << endl;
    cout << (dp[a] - 1)*(dp[b] - 1) << '\n';
    for(int i = 0; i < n; i++){
        tin[i] = fup[i] = dp[i] = used[i] = 0;
    }
    fl1 = 0, fl2 = 0;
    g.clear();
}

int main(){

    int t;
    cin >> t;
    while(t--){
        solve();
    }




}