/*

 ∧＿∧
( ･ω･｡)つ━☆・*。
⊂　 ノ 　　　・゜
しーＪ　　 Accepted

*/



// #pragma GCC optimize("O3")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

#define ll long long
#define all(x) begin(x), end(x)
#define x first
#define y second
#define int long long

using namespace std;
using namespace __gnu_pbds;

typedef long double ld;
template<typename T>
using kawaii_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

const ld PI = atan2(0, -1);

void seriy() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    cout << fixed << setprecision(14);
    #ifdef _offline
        freopen("input.txt", "r", stdin);
        freopen("output.txt", "w", stdout);
    #endif
}

const int MAXN = 2e5 + 100;
const int MAXM = 600;
const int INF = 1e9 + 7;
const int BASE = 47;
const int MOD = 1e9 + 7;
const int MAXLOG = 21;
const ld EPS = 1e-6;

vector<vector<int>> g, g2;
vector<bool> used;
vector<int> p, sz, act_sz;
int n, m, a, b, cnt = 0, cur = 0;

void dfs(int u) {
    used[u] = 1;
    for(auto v : g[u]) {
        if(!used[v]) {
            // cerr << u << " " << v << '\n';
            g2[u].push_back(v);
            g2[v].push_back(u);
            dfs(v);
        }
    }
}

void dfs2(int u) {
    used[u] = 1;
    cur++;
    // cerr << u << " " << g2.size() << '\n';
    for(auto v : g2[u]) {
        if(!used[v] && v != a && v != b) {
            dfs2(v);
        }
        else if(v == a) {
            cnt++;
        }
        else if(v == b) {
            cnt++;
        }
    }
}

int get(int a) {
    if(p[a] == a) {
        return a;
    }
    return p[a] = get(p[p[a]]);
}

void unite(int a, int b) {
    a = get(a);
    b = get(b);
    if(a != b) {
        if(sz[a] < sz[b]) {
            swap(a, b);
        }
        p[b] = a;
        sz[a] += sz[b];
        act_sz[a] += act_sz[b];
    }
}

signed main() {
    seriy();
    int q;
    cin >> q;
    while(q--) {
        cin >> n >> m >> a >> b;
        a--;
        b--;
        g2.clear();
        g.clear();
        g.resize(n);
        g2.resize(n);
        used.resize(n);
        for(int i = 0; i < m; i++) {
            int u, v;
            cin >> u >> v;
            u--;
            v--;
            g[u].push_back(v);
            g[v].push_back(u);
        }
        dfs(0);
        int sss = 0, kek = -1;
        fill(all(used), 0);
        for(int i = 0; i < n; i++) {
            if(!used[i] && i != a && i != b) {
                cnt = 0;
                cur = 0;
                dfs2(i);
                if(cnt == 2) {
                    kek = i;
                    sss = cur;
                }
            }
        }
        p.resize(n);
        sz.resize(n, 1);
        act_sz.resize(n, 1);
        for(int i = 0; i < n; i++) {
            p[i] = i;
        }
        for(int i = 0; i < g2.size(); i++) {
            for(auto j : g2[i]) {
                if(i != a && j != a && i != b && j != b) unite(i, j);
            }
        }
        if(kek != -1) act_sz[get(kek)] -= sss;
        for(int i = 0; i < g.size(); i++) {
            for(auto j : g[i]) {
                if(i != a && j != a && i != b && j != b) unite(i, j);
            }
        }
        set<int> st;
        for(int i = 0; i < n; i++) {
            if(i != a && i != b) st.insert(get(i));
        }
        vector<int> lol;
        for(auto i : st) {
            lol.push_back(act_sz[i]);
        }
        vector<int> sum(lol.size() + 1);
        for(int i = sum.size() - 1; i >= 0; i--) {
            sum[i] = sum[i + 1] + lol[i];
        }
        int ans = 0;
        for(int i = 0; i < sum.size(); i++) {
            ans += lol[i] * sum[i + 1];
        }
        cout << ans << '\n';
    }
    return 0;
}