#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 = 1010, INF = 0x7fffffff;
vector<int> G[50010];
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=0; 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 = 0;mem(sccno, 0);mem(pre, 0);mem(w, 0);mem(d, -1);mem(line, 0);for(int i=0; i<maxn; i++) G[i].clear();
}int dp(int u)
{int& ans = d[u];if(ans >= 0) return ans;ans = w[u];      //最后一个点后边就没有点了for(int i=1; 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=1; i<=m; i++){int u, v;scanf("%d%d", &u, &v);G[u].push_back(v);}for(int i=1; i<=n; i++)if(!pre[i])dfs(i);for(int i=1; i<=n; i++){w[sccno[i]]++;   //统计每个强连通分量里的点的个数for(int j=0; j<G[i].size(); j++)line[sccno[i]][sccno[G[i][j]]] = 1;}int res = 0;for(int i=1; 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 0;
}