#include<cstdio>

 #include<cstdlib>

 #include<cstring>

 #define Maxn 1010

 #define Maxm 50010

 struct node

 {

     int x,y,next;

 }t[Maxm];

 int first[Maxn],dfn[Maxn],low[Maxn],sta[Maxn],scc[Maxn],sum[Maxn];

 bool bj[Maxn],bj2[Maxn],map[Maxn][Maxn];

 int cnt,sl,cl;

 int mymin(int x,int y) {return x<y?x:y;}

 int mymax(int x,int y) {return x>y?x:y;}

 void ffind(int x)

 {

     dfn[x]=low[x]=++cnt;

     sta[++sl]=x;

     for(int i=first[x];i;i=t[i].next)

     {

         int y=t[i].y;

         if(dfn[y]==)

         {

             ffind(y);

             low[x]=mymin(low[x],low[y]);

         }

         else if(scc[y]==) low[x]=mymin(low[x],dfn[y]);

     }

     if(dfn[x]==low[x])

     {

         cl++;

         while()

         {

             int z=sta[sl--];

             scc[z]=cl;

             sum[cl]++;

             if(z==x) break;

         }

     }

 }

 int dfs(int x)

 {

     int ans=;

     bj[x]=;

     for(int i=;i<=cl;i++) if(map[x][i]==&&bj[i]==)

      ans=mymax(ans,dfs(i));

     ans+=sum[x];

     bj[x]=;

     return ans;

 }

 int main()

 {

     int T;

     scanf("%d",&T);

     while(T--)

     {

         int n,m,ans=;

         scanf("%d%d",&n,&m);

         memset(first,,sizeof(first));

         memset(dfn,,sizeof(dfn));

         memset(sum,,sizeof(sum));

         memset(bj,,sizeof(bj));

         memset(map,,sizeof(map));

         memset(scc,,sizeof(scc));

         cnt=;sl=;cl=;

         for(int i=;i<=m;i++)

         {

             int x,y;

             scanf("%d%d",&t[i].x,&t[i].y);

             t[i].next=first[t[i].x];first[t[i].x]=i;

         }

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

         for(int i=;i<=m;i++) if(scc[t[i].x]!=scc[t[i].y]) map[scc[t[i].x]][scc[t[i].y]]=;

         for(int i=;i<=cl;i++) ans=mymax(ans,dfs(i));

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

     }

     return ;

 }