C++ :

#include<iostream>
#include<cmath>
#include<cstring>
#include<stdio.h>
#include<algorithm>
#include<cassert>
using namespace std;
const int N=500100,mo=998244353;
struct bian{
	int next,point;
}b[N<<2];
int p[N],len,n,m,father[N],num[N],d[N],a[N],f[N];
void ade(int k1,int k2){
	b[++len]=(bian){p[k1],k2}; p[k1]=len;
}
void add(int k1,int k2){
	ade(k1,k2); ade(k2,k1);
}
void dfs(int k1){
	for (int i=p[k1];i!=-1;i=b[i].next){
		int j=b[i].point;
		if (d[j]==0){
			father[j]=k1; d[j]=d[k1]+1; dfs(j);
		}
	}
}
int dp[N];
int compare(int k1,int k2){
	return d[k1]<d[k2];
}
void getans(int k1,int flag=0){
	num[k1]=-1; dp[k1]=1; int tot=0;
	for (int i=p[k1];i!=-1;i=b[i].next){
		int j=b[i].point;
		if (num[j]==1){
			getans(j); dp[k1]=1ll*dp[k1]*dp[j]%mo; tot++;
		}
	}
	if (tot==0) return;
	if (flag==0)
		dp[k1]=1ll*dp[k1]*(f[tot]+1ll*tot*f[tot-1]%mo)%mo;
	else dp[k1]=1ll*dp[k1]*f[tot]%mo;
}
int getfather(int k1){
	if (a[k1]==k1) return k1; return a[k1]=getfather(a[k1]);
}
void solve(){
	scanf("%d%d",&n,&m);
	for (int i=1;i<=n;i++) p[i]=-1,father[i]=num[i]=d[i]=0,a[i]=i;
	len=-1;
	for (int i=1;i<=m;i++){
		int k1,k2; scanf("%d%d",&k1,&k2); add(k1,k2); //a[getfather(k1)]=getfather(k2);
	}
/*	for (int i=1;i<=n;i++){
		assert(getfather(i)==getfather(1));
	}
	for (int i=1;i<=n;i++) a[i]=i;*/
	d[1]=1; dfs(1); sort(a+1,a+n+1,compare);
//	cout<<"asd"<<endl;
//	for (int i=1;i<=n;i++) cout<<father[i]<<" "; cout<<endl;
	for (int i=1;i<=m;i++){
		int u=b[(i-1)<<1].point,v=b[(i<<1)-1].point;
		if (d[u]<d[v]) swap(u,v);
//		cout<<u<<" "<<v<<endl;
		while (u!=v){
			num[u]++;
			if (num[u]>2){
				printf("0\n"); return;
			}		 
			u=father[u];
		}
	}
	int ans=1;
	for (int i=1;i<=n;i++)
		if (num[a[i]]!=-1){
		//	cout<<"fa "<<a[i]<<endl;
			getans(a[i],1); ans=1ll*ans*dp[a[i]]%mo;
		}
	printf("%d\n",ans);
}
int main(){
	//freopen("cactus.in","r",stdin);
	//freopen("cactus.out","w",stdout);
	f[0]=1; f[1]=1;
	for (int i=2;i<=500000;i++) f[i]=(f[i-1]+1ll*(i-1)*f[i-2])%mo;
	int t; scanf("%d",&t);
	for (;t;t--){
		solve();
	}
	return 0;
}