/*Author: Satyajeet Singh, Delhi Technological University*/
    import java.io.*;
    import java.util.*;
    import java.text.*; 
    import java.lang.*;
    import java.math.*;
public class Main{
/*********************************************Constants******************************************/
    static PrintWriter out=new PrintWriter(new OutputStreamWriter(System.out));        
    static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    static long mod=(long)1e9+7;
    static long mod1=998244353;
    static boolean sieve[];
    static ArrayList<Integer> primes;
    static long factorial[],invFactorial[];
    static ArrayList<Integer> graph[];
    static int pptr=0;
    static String st[];
/****************************************Solutions Begins***************************************/
    static int point=-1;
    static boolean vis[];
    static boolean forbidden[];
    static int end=0;
    static boolean dfs1(int start){
        //debug(start);
        if(start==end){
            forbidden[start]=true;
            vis[start]=true;
            return true;
        }
        vis[start]=true;
        for(int u:graph[start]){
            if(vis[u])continue;
            boolean cur=dfs1(u);
            if(u==end){
                point=start;
            }
            if(cur){
                forbidden[u]=true;
                return true;
            }
        }
        return false;
    }
    static class DSU{
        int dsu[];
        long dsu_size[];
        int unconnected=0;
        long curr=0;
        DSU(int n){
            dsu=new int[n];
            dsu_size=new long[n];
            Arrays.fill(dsu,-1);
            Arrays.fill(dsu_size,0l);
            unconnected=n-1;
            for(int i=1;i<=n-1;i++){
                makeSet(i);
            }
        }
        void makeSet(int v){
            dsu[v]=v;
            dsu_size[v]=1;
        }
        int findSet(int v){
            if(dsu[v]==v){
                return v;
            }
            int v1=findSet(dsu[v]);
            dsu[v]=v1;
            return v1;
        }
        long getSize(int s1){
            int a=findSet(s1);
            return dsu_size[a];
        }
        void union(int s1,int s2){
            int a=findSet(s1);
            int b=findSet(s2);
            if(a!=b){
                unconnected--;
                if(dsu_size[a]>dsu_size[b]){
                    int temp=a;
                    a=b;
                    b=temp;
                }
                dsu[a]=b;
                dsu_size[b]+=dsu_size[a];
            }
        }
    }
    public static void main(String[] args) throws Exception{
        nl();
        int t=pi();
        while(t-->0){
            nl();
            int n=pi();
            int m=pi();
            int a=pi();
            int b=pi();
            end=b;
            int edge[]=new int[2*m];
            int e=0;
            Makegraph(n+1);
            for(int i=1;i<=m;i++){
                nl();
                int x=pi();
                int y=pi();
                addEdge(x,y);
                addEdge(y,x);
                edge[e++]=x;
                edge[e++]=y;
            }
            point=-1;
            vis=new boolean[n+1];
            forbidden=new boolean[n+1];
            dfs1(a);
            forbidden[a]=true;
            forbidden[b]=true;
            //debug(forbidden);
            DSU d=new DSU(n+1);
            for(int i=0;i<e;i+=2){
                int x=edge[i];
                int y=edge[i+1];
                if(x==end&&y==point||x==point&&y==end){
                    ;
                }
                else{
                    d.union(x,y);
                }
            }
            //debug(forbidden);
            if(d.findSet(a)==d.findSet(b)){
                out.println(0);
            }
            else{
                long sz1=0;
                long sz2=0;
                int f1=d.findSet(a);
                int f2=d.findSet(b);
                for(int i=1;i<=n;i++){
                    if(forbidden[i])continue;
                    if(d.findSet(i)==f1)sz1++;
                    else sz2++;
                }
                //debug(sz1,sz2);
                out.println(sz1*sz2);
            }
        }
/****************************************Solutions Ends**************************************************/
        out.flush();
        out.close();
    }
/****************************************Template Begins************************************************/
    static void nl() throws Exception{
        pptr=0;
        st=br.readLine().split(" ");
    }
    static void nls() throws Exception{
        pptr=0;
        st=br.readLine().split("");
    }
    static int pi(){
        return Integer.parseInt(st[pptr++]);
    }
    static long pl(){
        return Long.parseLong(st[pptr++]);
    }
    static double pd(){
        return Double.parseDouble(st[pptr++]);
    }
    static String ps(){
        return st[pptr++];
    }
/***************************************Precision Printing**********************************************/
    static void printPrecision(double d){
        DecimalFormat ft = new DecimalFormat("0.000000000000"); 
        out.print(ft.format(d));
    }
/**************************************Bit Manipulation**************************************************/
    static void printMask(long mask){
        System.out.println(Long.toBinaryString(mask));
    }
    static int countBit(long mask){
        int ans=0;
        while(mask!=0){
            mask&=(mask-1);
            ans++;
        }
        return ans;
    }
/******************************************Graph*********************************************************/
    static void Makegraph(int n){
        graph=new ArrayList[n];
        for(int i=0;i<n;i++){
            graph[i]=new ArrayList<>();
        }
    }
    static void addEdge(int a,int b){
        graph[a].add(b);
    }
    // static void addEdge(int a,int b,int c){
    //     graph[a].add(new Pair(b,c));
    // }    
/*********************************************PAIR********************************************************/
    static class Pair implements Comparable<Pair> {
        int u;
        int v;
        int index=-1;
        public Pair(int u, int v) {
            this.u = u;
            this.v = v;
        }
        public int hashCode() {
            int hu = (int) (u ^ (u >>> 32));
            int hv = (int) (v ^ (v >>> 32));
            return 31 * hu + hv;
        }
        public boolean equals(Object o) {
            Pair other = (Pair) o;
            return u == other.u && v == other.v;
        }
        public int compareTo(Pair other) {
            if(index!=other.index)
                return Long.compare(index, other.index);
            return Long.compare(v, other.v)!=0?Long.compare(v, other.v):Long.compare(u, other.u);
        }
        public String toString() {
            return "[u=" + u + ", v=" + v + "]";
        }
    }
/******************************************Long Pair*******************************************************/
    static class Pairl implements Comparable<Pairl> {
            long u;
            long v;
            int index=-1;
            public Pairl(long u, long v) {
                this.u = u;
                this.v = v;
            }
            public int hashCode() {
                int hu = (int) (u ^ (u >>> 32));
                int hv = (int) (v ^ (v >>> 32));
                return 31 * hu + hv;
            }
            public boolean equals(Object o) {
                Pairl other = (Pairl) o;
                return u == other.u && v == other.v;
            }
            public int compareTo(Pairl other) {
                if(index!=other.index)
                    return Long.compare(index, other.index);
                return Long.compare(v, other.v)!=0?Long.compare(v, other.v):Long.compare(u, other.u);
            }
            public String toString() {
                return "[u=" + u + ", v=" + v + "]";
            }
        }
/*****************************************DEBUG***********************************************************/
    public static void debug(Object... o){
        System.out.println(Arrays.deepToString(o));
    }
/************************************MODULAR EXPONENTIATION***********************************************/
    static long modulo(long a,long b,long c){
        long x=1;
        long y=a%c;
        while(b > 0){
            if(b%2 == 1){
                x=(x*y)%c;
            }
            y = (y*y)%c; // squaring the base
            b /= 2;
        }
        return  x%c;
    }
/********************************************GCD**********************************************************/
    static long gcd(long x, long y){
        if(x==0)
            return y;
        if(y==0)
            return x;
        long r=0, a, b;
        a = (x > y) ? x : y; // a is greater number
        b = (x < y) ? x : y; // b is smaller number
        r = b;
        while(a % b != 0){
            r = a % b;
            a = b;
            b = r;
        }
        return r;
    }
/******************************************SIEVE**********************************************************/
    static void sieveMake(int n){
        sieve=new boolean[n];
        Arrays.fill(sieve,true);
        sieve[0]=false;
        sieve[1]=false;
        for(int i=2;i*i<n;i++){
            if(sieve[i]){
                for(int j=i*i;j<n;j+=i){
                    sieve[j]=false;
                }
            }
        }
        primes=new ArrayList<Integer>();
        for(int i=0;i<n;i++){
            if(sieve[i]){
                primes.add(i);
            }
        }        
    }
/********************************************End***********************************************************/
}