#include<iostream>

 #include<cstdio>

 #include<cstring>

 #include<map>

 #include<set>

 #include<stack>

 #include<deque>

 #include<bitset>

 #include<unordered_map>

 #include<unordered_set>

 #include<queue>

 #include<cstdlib>

 #include<ctype.h>

 #include<ctime>

 #include<functional>

 #include<algorithm>

 #include<bits/stdc++.h>

 using namespace std;

 #define LL long long

 #define pii pair<int,int>

 #define mp make_pair

 #define pb push_back

 #define fi first

 #define se second

 #define inf 0x3f3f3f3f

 #define debug puts("debug")

 #define mid ((L+R)>>1)

 #define lc (id<<1)

 #define rc (id<<1|1)

 const int maxn=;

 const int maxm=;

 const double PI=acos(-1.0);

 const double eps=1e-;

 const LL mod=1e9+;

 LL gcd(LL a,LL b){return b==?a:gcd(b,a%b);}

 LL lcm(LL a,LL b){return a/gcd(a,b)*b;}

 LL qpow(LL a,LL b,LL c){LL r=; for(;b;b>>=,a=a*a%c)if(b&)r=r*a%c;return r;}

 template<class T>

 void prt(T v){for(auto x:v)cout<<x<<' ';cout<<endl;}

 struct Edge{int u,v,w,next;};

 vector<int>g[maxn],g2[maxn];

 int f[maxn],dfn[maxn],low[maxn],scc[maxn],tot[maxn],sum=,scc_cnt=;

 stack<int>S;

 void dfs(int u){

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

     S.push(u);

     for(int v:g[u]){

         if(!dfn[v]){

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

         }else if(!scc[v]){

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

         }

     }

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

         ++scc_cnt;

         for(;;){

             int x=S.top();S.pop();

             scc[x]=scc_cnt;

             tot[scc_cnt]++;

             if(x==u)break;

         }

     }

 }

 int cal(int u){

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

     f[u]=tot[u];

     int maxx=;

     for(int v:g2[u]){

         maxx=max(maxx,cal(v));

     }

     return f[u]=f[u]+maxx;

 }

 int main(){

     int t,n,m,i,j,u,v;

     cin>>t;

     while(t--){

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

         for(i=;i<=n;++i)g[i].clear(),g2[i].clear(),tot[i]=low[i]=dfn[i]=scc[i]=;

         sum=scc_cnt=;

         while(!S.empty())S.pop();

         while(m--){

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

             g[u].pb(v);

         }

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

             if(!dfn[i]){

                 dfs(i);

             }

         }

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

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

             for(int v:g[u]){

                 if(scc[u]!=scc[v]){

                     //cout<<scc[v]<<' '<<scc[u]<<

                     g2[scc[v]].pb(scc[u]);

                 }

             }

         }

         int ans=;

         for(i=;i<=scc_cnt;++i){

             f[i]=cal(i);

             if(f[i]>ans)ans=f[i];

         }

         cout<<ans<<endl;

     }

     return ;

 }

 /*

 1

 5 5

 1 2

 2 3

 3 1

 4 1

 5 2

 */