#include<bits/stdc++.h>
using namespace std;
const int N=1005,M=6005;
struct edge{int from,to,next;}e[M],e2[M];
int head[N],head2[N],dfn[N],low[N],scc[N],in[N],out[N];
int dfncnt,sccnum,n,m,cnt,cnt2;
stack<int> st;
void init(){
    dfncnt=sccnum=cnt=cnt2=0;
    memset(dfn,0,sizeof(dfn));
    memset(low,0,sizeof(low));
    memset(scc,0,sizeof(scc));
    memset(head,0,sizeof(head));
    memset(head2,0,sizeof(head2));
    memset(in,0,sizeof(in));
    memset(out,0,sizeof(out));
    while(!st.empty()) st.pop();
}
void addedge(int u,int v){
    e[++cnt]=(edge){u,v,head[u]};
    head[u]=cnt;
}
void addedge2(int u,int v){
    e2[++cnt2]=(edge){u,v,head2[u]};
    head2[u]=cnt2;
}
void tarjan(int u){
    dfn[u]=low[u]=++dfncnt;
    st.push(u);
    for(int i=head[u];i;i=e[i].next){
        int v=e[i].to;
        if(!dfn[v]){
            tarjan(v);
            low[u]=min(low[u],low[v]);
        }
        else if(!scc[v]){
            low[u]=min(low[u],dfn[v]);
        }
    }
    if(low[u]==dfn[u]){
        sccnum++;
        while(1){
            int x=st.top(); st.pop();
            scc[x]=sccnum;
            if(x==u) break;
        }
    }
}
bool check(){
    if(sccnum==1) return true;
    int start=0, end=0;
    for(int i=1;i<=sccnum;i++){
        if(!in[i]) start++;
        if(!out[i]) end++;
        if(in[i]>1 || out[i]>1) return false;
    }
    if(start!=1 || end!=1) return false;
    
    queue<int> q;
    vector<bool> vis(sccnum+1,false);
    for(int i=1;i<=sccnum;i++){
        if(!in[i]){
            q.push(i);
            vis[i]=true;
            break;
        }
    }
    
    int cntv=0;
    while(!q.empty()){
        int u=q.front(); q.pop();
        cntv++;
        for(int i=head2[u];i;i=e2[i].next){
            int v=e2[i].to;
            if(!vis[v]){
                vis[v]=true;
                q.push(v);
            }
        }
    }
    return cntv==sccnum;
}
int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int T; cin>>T;
    while(T--){
        cin>>n>>m;
        init();
        for(int i=1;i<=m;i++){
            int u,v; cin>>u>>v;
            addedge(u,v);
        }
        
        for(int i=1;i<=n;i++){
            if(!dfn[i]) tarjan(i);
        }
        for(int i=1;i<=cnt;i++){
            int u=scc[e[i].from], v=scc[e[i].to];
            if(u!=v){
                addedge2(u,v);
                out[u]++;
                in[v]++;
            }
        }
        
        cout<<(check()?"Yes":"No")<<endl;
    }
    return 0;
}