//

//  main.cpp

//  最大团

//

//  Created by Candy on 02/11/2016.

//  Copyright © 2016 Candy. All rights reserved.

//

#include <iostream>

#include <cstdio>

#include <algorithm>

#include <cstring>

#define C(x) memset(x,0,sizeof(x))

using namespace std;

const int N=1e3+,M=5e4+;

inline int read(){

    char c=getchar();int x=,f=;

    while(c<''||c>''){if(c=='-')f=-;c=getchar();}

    while(c>=''&&c<=''){x=x*+c-'';c=getchar();}

    return x*f;

}

int T,n,m,u,v;

struct edge{

    int v,ne;

}e[M];

int h[N],cnt=;

inline void ins(int u,int v){

    cnt++;

    e[cnt].v=v;e[cnt].ne=h[u];h[u]=cnt;

}

int dfn[N],low[N],belong[N],dfc,scc,size[N];

int st[N],top;

void dfs(int u){

    dfn[u]=low[u]=++dfc;

    st[++top]=u;

    for(int i=h[u];i;i=e[i].ne){

        int v=e[i].v;

        if(!dfn[v]){

            dfs(v);

            low[u]=min(low[u],low[v]);

        }else if(!belong[v])

                low[u]=min(low[u],dfn[v]);

    }

    if(low[u]==dfn[u]){

        scc++;

        while(true){

            int x=st[top--];

            belong[x]=scc;

            size[scc]++;

            if(x==u) break;

        }

    }

}

void SCC(){

    dfc=scc=;

    C(dfn);C(low);C(belong);C(size);

    top=;

    for(int i=;i<=n;i++) if(!dfn[i]) dfs(i);

}

edge es[N];

int hs[N],cs=;

inline void inss(int u,int v){

    cs++;

    es[cs].v=v;es[cs].ne=hs[u];hs[u]=cs;

}

void buildGraph(){

    cs=;

    C(hs);

    for(int u=;u<=n;u++){

        int a=belong[u];

        for(int i=h[u];i;i=e[i].ne){

            int b=belong[e[i].v];

            if(a!=b) inss(a,b);

        }

    }

}

int f[N];

int dp(int u){

    if(f[u]!=-) return f[u];

    f[u]=size[u];

    int mx=;

    for(int i=hs[u];i;i=es[i].ne){

        int v=es[i].v;//printf("dp %d v %d\n",u,v);

        mx=max(mx,dp(v));

    }

    return f[u]+=mx;

}

int main(int argc, const char * argv[]) {

    T=read();

    while(T--){

        n=read();m=read();

        cnt=;memset(h,,sizeof(h));

        for(int i=;i<=m;i++){u=read();v=read();ins(u,v);}

        SCC();

        buildGraph();

        memset(f,-,sizeof(f));

        int ans=;

        for(int i=;i<=scc;i++){

            if(f[i]==-) dp(i);

            ans=max(ans,f[i]);

        }

        printf("%d\n",ans);

    }

    return ;

}