#include <bits/stdc++.h> using namespace std; #define ii pair<int, int> #define iii pair<int, ii> #define vii vector<ii> #define viii vector<iii> #define MASK(i) (1LL << (i)) #define BIT(x, i) (((x) >> (i)) & 1) void minimize(int &u, int v) { if (v < u) u = v; } void maximize(int &u, int v) { if (v > u) u = v; } void minimizell(long long &u, long long v) { if (v < u) u = v; } void maximizell(long long &u, long long v) { if (v > u) u = v; } const int maxN = 1e5 + 2; const int mod = 1e9 + 7; const int inf = 1e9 + 8; const long long infll = 1e18 + 8; const int LOG = 19; const int inverse_mod = 1e9 + 5; int N, M; int num[maxN], low[maxN], timeDfs, tt, scc[maxN], f[maxN]; bool exist[maxN]; vector<int> adj[maxN], graph[maxN]; stack<int> st; void dfs(int u) { st.push(u); num[u] = low[u] = ++timeDfs; for (int v : adj[u]) { if (scc[v] > 0) continue; if (num[v] == 0) { dfs(v); minimize(low[u], low[v]); } else { minimize(low[u], num[v]); } } if (num[u] == low[u]) { ++tt; while (!st.empty()) { int p = st.top(); st.pop(); scc[p] = tt; if (p == u) break; } } } void solve(int u) { f[u] = 0; for (int v : graph[u]) { if (f[v] == -1) solve(v); maximize(f[u], f[v] + 1); } } void init() { int T; cin >> T; while (T--) { cin >> N >> M; for (int i = 1; i <= N; ++i) { num[i] = low[i] = 0; adj[i].clear(); scc[i] = 0; graph[i].clear(); f[i] = 0; exist[i] = false; } timeDfs = 0; tt = 0; int u, v; for (int i = 1; i <= M; ++i) { cin >> u >> v; exist[u] = exist[v] = true; adj[u].push_back(v); } for (int i = 1; i <= N; ++i) if (num[i] == 0 and exist[i]) dfs(i); for (int i = 1; i <= tt; ++i) f[i] = -1; for (int i = 1; i <= N; ++i) { for (int j : adj[i]) { if (scc[i] != scc[j]) { graph[scc[i]].push_back(scc[j]); } } } for (int i = 1; i <= tt; ++i) if (f[i] == -1) solve(i); bool ok = false; for (int i = 1; i <= tt; ++i) { if (f[i] == tt - 1) { cout << "YES\n"; ok = true; break; } } if (ok == false) cout << "NO\n"; } } int main() { // freopen(".INP","r",stdin); // freopen(".OUT","w",stdout); ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0); init(); return 0; }