#include <iostream>

#include <cstdio>

#include <sstream>

#include <cstring>

#include <map>

#include <set>

#include <vector>

#include <stack>

#include <queue>

#include <algorithm>

#include <cmath>

#define rap(a, n) for(int i=a; i<=n; i++)

#define MOD 2018

#define LL long long

#define ULL unsigned long long

#define Pair pair<int, int>

#define mem(a, b) memset(a, b, sizeof(a))

#define _  ios_base::sync_with_stdio(0),cin.tie(0)

//freopen("1.txt", "r", stdin);

using namespace std;

const int maxn = , INF = 0x7fffffff;

vector<int> G[];

int pre[maxn], low[maxn], sccno[maxn], dfs_clock, scc_cnt;

int w[maxn], line[maxn][maxn], d[maxn];

stack<int> s;

void dfs(int u)

{

    pre[u] = low[u] = ++dfs_clock;

    s.push(u);

    for(int i=; i<G[u].size(); i++)

    {

        int v = G[u][i];

        if(!pre[v])

        {

            dfs(v);

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

        }

        else if(!sccno[v])

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

    }

    if(low[u] == pre[u])

    {

        scc_cnt++;

        for(;;)

        {

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

            sccno[x] = scc_cnt;

            if(x == u) break;

        }

    }

}

void init()

{

    dfs_clock = scc_cnt = ;

    mem(sccno, );

    mem(pre, );

    mem(w, );

    mem(d, -);

    mem(line, );

    for(int i=; i<maxn; i++) G[i].clear();

}

int dp(int u)

{

    int& ans = d[u];

    if(ans >= ) return ans;

    ans = w[u];      //最后一个点后边就没有点了

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

        if(u != i && line[u][i])

            ans = max(ans, dp(i) + w[u]);

    return ans;

}

int main()

{

    int T;

    scanf("%d", &T);

    while(T--)

    {

        init();

        int n, m;

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

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

        {

            int u, v;

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

            G[u].push_back(v);

        }

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

            if(!pre[i])

                dfs(i);

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

        {

            w[sccno[i]]++;   //统计每个强连通分量里的点的个数

            for(int j=; j<G[i].size(); j++)

                line[sccno[i]][sccno[G[i][j]]] = ;

        }

        int res = ;

        for(int i=; i<=scc_cnt; i++)  // 以每一个点为起点 去找最长路

            res = max(res, dp(i));

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

    }

    return ;

}