#include<bits/stdc++.h>
using namespace std;
int n_,n;
#define db double
#define pb push_back
int qc[4010],L[4010],R[4010],cn;
int ct[4010];
vector<int>g[4010];
db dis[4010];
bool vis[4010];
const int mod=998244353;
int qpow(int a,int b){
    int c=1;
    for(;b;b>>=1){
        if(b&1)c=1ll*a*c%mod;
        a=1ll*a*a%mod;
    }
    return c;
}
bool chk(db X){
    queue<int>q;
    for(int i=1;i<=cn;i++)dis[i]=0,ct[i]=0,q.push(i),vis[i]=1;
    while(!q.empty()){
        int u=q.front();q.pop();vis[u]=0;
        ct[u]++;if(ct[u]>cn)return 0;
        if(u<cn){
            if(dis[u+1]>dis[u]){
                dis[u+1]=dis[u];
                if(!vis[u+1])
                vis[u+1]=1,q.push(u+1);
            }
        }
        for(int v:g[u]){
            db w=(u<v)?(-1):X;
            if(dis[v]>dis[u]+w){
                dis[v]=dis[u]+w;
                if(!vis[v])vis[v]=1,q.push(v);
            }
        }
    }
    return 1;
}
const db eps=1e-7;
#define ll long long
void sol(){
    scanf("%d%d",&n_,&n);
    cn=0;
    for(int i=1;i<=n;i++)
        scanf("%d%d",&L[i],&R[i]),L[i]--,qc[++cn]=L[i],qc[++cn]=R[i];
    sort(qc+1,qc+cn+1);cn=unique(qc+1,qc+cn+1)-qc-1;
    for(int i=1;i<=cn;i++)g[i].clear();
    for(int i=1;i<=n;i++)L[i]=lower_bound(qc+1,qc+cn+1,L[i])-qc,R[i]=lower_bound(qc+1,qc+cn+1,R[i])-qc,
    g[L[i]].pb(R[i]),g[R[i]].pb(L[i]);
    db l=0,r=n*5;int cnt=30;
    while(cnt--){
        db mi=(l+r)/2;
        if(chk(mi))r=mi;
        else l=mi;
    }
    for(int i=1;i<=n*5;i++){
        db p=l*i;ll z=(ll)p;
        while(z>p+0.5)z--;
        while(z<p-0.5)z++;
        if(abs(z-p)<eps)
        {printf("%lld\n",z%mod*qpow(i,mod-2)%mod);
        return;}
    }
}
int main(){
    int T;scanf("%d",&T);while(T--)sol();
}