/*每个环 要么不选 要么全选 可缩点 就得到一个GAD图 然后搞搞算出最大路径*/

#include<iostream>

#include<cstdio>

#include<cstring>

#define maxn 100010

using namespace std;

int T,n,m,num,head[maxn],low[maxn],dfn[maxn],s[maxn],top,vi[maxn];

int sum,belong[maxn],Head[maxn],Num,ans,f[maxn],topt,dp[maxn];

struct node{int v,pre;}e[maxn];

struct Node{int v,pre;}E[maxn];

void add(int from,int to)

{

    e[num].v=to;

    e[num].pre=head[from];

    head[from]=num++;

}

void Add(int from,int to)

{

    E[Num].v=to;

    E[Num].pre=Head[from];

    Head[from]=Num++;

}

void Tarjan(int x)

{

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

    s[++top]=x;f[x]=;

    for(int i=head[x];i!=-;i=e[i].pre)

      {

          int v=e[i].v;

          if(dfn[v]==)

            {

                Tarjan(v);low[x]=min(low[x],low[v]);

          }

        else if(f[v])low[x]=min(low[x],dfn[v]);

      }

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

      {

          sum++;

          while(x!=s[top])

            {

                f[s[top]]=;belong[s[top]]=sum;top--;vi[sum]++;

          }

          f[s[top]]=;belong[s[top]]=sum;top--;vi[sum]++;

      }

}

int Dfs(int x)

{

    if(dp[x])return dp[x];

    int r=;

    for(int i=Head[x];i!=-;i=E[i].pre)

      {

          int v=E[i].v;

          r=max(r,Dfs(v));

      }

    return dp[x]=r+vi[x];

}

int main()

{

    scanf("%d",&T);

    while(T--)

      {

        memset(belong,,sizeof(belong));

          memset(head,-,sizeof(head));

          memset(Head,-,sizeof(Head));

          memset(low,,sizeof(low));

          memset(dfn,,sizeof(dfn));

          memset(dp,,sizeof(dp));

          memset(vi,,sizeof(vi));

          memset(f,,sizeof(f));

          memset(s,,sizeof(s));

          num=Num=topt=sum=ans=;

          int u,v;

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

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

            {

                scanf("%d%d",&u,&v);

                add(u,v);

          }

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

          if(dfn[i]==)

            Tarjan(i);

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

          for(int i=head[u];i!=-;i=e[i].pre)

            {

              int U=belong[u],V=belong[e[i].v];

              if(U!=V)Add(U,V);

            }

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

          ans=max(ans,Dfs(i));

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

      }

}