
import java.util.*;
import java.lang.*;
import java.lang.reflect.Array;
import java.io.*;
import java.math.*;
import java.text.DecimalFormat;
public class Prac{     
    static class InputReader { 
        private final InputStream stream;
	private final byte[] buf = new byte[8192];
	private int curChar, snumChars;
 	public InputReader(InputStream st) {
            this.stream = st;
	} 
	public int read() {
            if (snumChars == -1)
	 	throw new InputMismatchException();
            if (curChar >= snumChars) {
		curChar = 0;
                try {
                    snumChars = stream.read(buf);
		} 
                catch (IOException e) {
                    throw new InputMismatchException();
           	}
		if (snumChars <= 0)
                    return -1;
            }
            return buf[curChar++];
	}
        public int ni() {
            int c = read();
            while (isSpaceChar(c)) {
               	c = read();
            }
            int sgn = 1;
            if (c == '-') {
		sgn = -1;
		c = read();
            }
            int res = 0;
            do {
		res *= 10;
		res += c - '0';
		c = read();
            } while (!isSpaceChar(c));
            return res * sgn;
	} 
	public long nl() {
            int c = read();
            while (isSpaceChar(c)) {
            c = read();
            }
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            long res = 0;
            do {
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res * sgn;
	} 
	public int[] nia(int n) {
            int a[] = new int[n];
            for (int i = 0; i < n; i++) {
		a[i] = ni();
            }
            return a;
	} 
	public String rs() {
            int c = read();
            while (isSpaceChar(c)) {
		c = read();
            }
            StringBuilder res = new StringBuilder();
            do {
		res.appendCodePoint(c);
                    c = read();
            } while (!isSpaceChar(c));
            return res.toString();
	}
	public String nextLine() {
            int c = read();
            while (isSpaceChar(c))
		c = read();
            StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = read();
            } while (!isEndOfLine(c));
            return res.toString();
        } 
	public boolean isSpaceChar(int c) {
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
	}
 
	private boolean isEndOfLine(int c) {
            return c == '\n' || c == '\r' || c == -1;
	} 
    }
    static PrintWriter w = new PrintWriter(System.out);
    static long mod=998244353L,mod1=1000000007;
    
    static HashSet<Integer> arr[];
    static boolean v[],ce=false;
    static int n,m,a,b,cou=0;
    static boolean dfsA(int i,int p){
        if(i==b){
            ce=true;
            return true;
            
        }
        if(v[i])return false;
        v[i]=true;
        boolean f=false;
        HashSet<Integer> temp=new HashSet<>();
        for(int j:arr[i]){
            if(j!=p&&dfsA(j,i)){
                temp.add(j);
                f=true;
            }
        }
        for(int j:temp){
            arr[i].remove(j);
            arr[j].remove(i);
        }
        return f;
    }
    static void dfs(int i,int p){
        if(v[i])return;
        v[i]=true;
        cou++;
        for(int j:arr[i]){
            if(j!=p)dfs(j,i);
        }
    }
    public static void main (String[] args)throws IOException{
        InputReader sc=new InputReader(System.in);
//        int t=sc.ni();
//        while(t-->0){
//            char arr[]=sc.nextLine().toCharArray();
//            
//            for(int i=2;i<arr.length;i++){
//                int j=i-2,k=i-1,l=i;
//                while(arr[j]=='o'&&arr[k]=='n'&&arr[l]=='e')
//            }
//        }
        int t=sc.ni();
        while(t-->0){
            
            n=sc.ni();m=sc.ni();a=sc.ni();b=sc.ni();
            arr=new HashSet[n+1];
            v=new boolean[n+1];
            for(int i=0;i<=n;i++)arr[i]=new HashSet<>();
            for(int i=0;i<m;i++){
                int u=sc.ni(),v=sc.ni();
                arr[u].add(v);
                arr[v].add(u);
            }
            cou=0;
            dfsA(a,a);
            Arrays.fill(v,false);
            cou=0;
            dfs(a,a);
            long ans=1;
            ans*=(cou-1);
            cou=0;
            dfs(b,b);
            w.println(!ce?0:ans*(cou-1));
        }
        w.close();
    }
}