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#include <bits/stdc++.h>
using namespace std;
const int MAXN = 201000;
const int MAXM = 1001000;
// 无权有向图
struct Graph {
    struct Edge {
        int to, next;
    } edge[MAXM];
    int head[MAXN];
    int tot;
    void init(int n) {
        tot = 0;
        memset(head, -1, sizeof(int) * (n + 1));
    }
    void add_edge(int from, int to) {
        edge[tot].to = to;
        edge[tot].next = head[from];
        head[from] = tot++;
    }
} graph;
void solve() {
    int T;
    cin >> T;
    for (int ts = 0; ts < T; ++ts) {
        int n, m, a, b;
        cin >> n >> m >> a >> b;
        graph.init(n);
        for (int i = 0; i < m; ++i) {
            int u, v;
            cin >> u >> v;
            graph.add_edge(u, v);
            graph.add_edge(v, u);
        }
        bool vis[MAXN];
        queue<int> q;
        int a_cnt = n - 2, b_cnt = n - 2;
        memset(vis, false, sizeof(bool) * (n + 1));
        q.push(a);
        vis[a] = true;
        while (!q.empty()) {
            int cur = q.front();
            q.pop();
            for (int i = graph.head[cur]; i != -1; i = graph.edge[i].next) {
                if (!vis[graph.edge[i].to] && graph.edge[i].to != b) {
                    vis[graph.edge[i].to] = true;
                    q.push(graph.edge[i].to);
                    a_cnt--;
                }
            }
        }
        memset(vis, false, sizeof(bool) * (n + 1));
        q.push(b);
        vis[b] = true;
        while (!q.empty()) {
            int cur = q.front();
            q.pop();
            for (int i = graph.head[cur]; i != -1; i = graph.edge[i].next) {
                if (!vis[graph.edge[i].to] && graph.edge[i].to != a) {
                    vis[graph.edge[i].to] = true;
                    q.push(graph.edge[i].to);
                    b_cnt--;
                }
            }
        }
        cout << 1ll * a_cnt * b_cnt << endl;
    }
}
int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
#ifdef ACM_LOCAL
    freopen("in.txt", "r", stdin);
    freopen("out.txt", "w", stdout);
    long long test_index_for_debug = 1;
    char acm_local_for_debug;
    while (cin >> acm_local_for_debug) {
        cin.putback(acm_local_for_debug);
        if (test_index_for_debug > 20) {
            throw runtime_error("Check the stdin!!!");
        }
        auto start_clock_for_debug = clock();
        solve();
        auto end_clock_for_debug = clock();
        cout << "Test " << test_index_for_debug << " successful" << endl;
        cerr << "Test " << test_index_for_debug++ << " Run Time: "
             << double(end_clock_for_debug - start_clock_for_debug) / CLOCKS_PER_SEC << "s" << endl;
        cout << "--------------------------------------------------" << endl;
    }
#else
    solve();
#endif
    return 0;
}