#include<bits/stdc++.h>
using namespace std;
vector<int>g[401000];int m;
map<int,int>fx,fy;
#define pb push_back
int X[400100],Y[401000],dfn[400100];
int U[401000],V[400100];bool vis[401000];
int ans,A[400100],B[401000],n1,n2;
void lj(int x,int y){
    ans++,A[ans]=x,B[ans]=y,vis[x]=vis[y]=1;
}
#define pb push_back
void ad(int u,int v,int w){U[w]=u,V[w]=v,g[u].pb(w),g[v].pb(w);}
void dfs(int x,int o){
    dfn[x]=++dfn[0];
    vector<int>Z;
    for(int i:g[x]){
        int v=U[i]^V[i]^x;
        if(!dfn[v]){
            dfs(v,i);
            if(!vis[i])Z.pb(i);
        }
        else if(dfn[x]<dfn[v])Z.pb(i);
    }
    while(Z.size()>=2){
        int x=Z.back();Z.pop_back();
        int y=Z.back();Z.pop_back();
        lj(x,y);
    }
    if(o&&!Z.empty())lj(o,Z.back());
}
void sol(){
    scanf("%d",&m);m*=2;
    fx.clear(),fy.clear();
    for(int i=1;i<=m;i++){
        vis[i]=0;
        scanf("%d%d",&X[i],&Y[i]);
        if(!fx[X[i]])fx[X[i]]=++n1;
        X[i]=fx[X[i]];
        if(!fy[Y[i]])fy[Y[i]]=++n2;
        Y[i]=fy[Y[i]];
    }
    dfn[0]=0;
    for(int i=1;i<=n1+n2;i++)g[i].clear(),dfn[i]=0;
    for(int i=1;i<=m;i++)ad(X[i],n1+Y[i],i);
    ans=0;for(int i=1;i<=n1+n2;i++)if(!dfn[i])dfs(i,0);
    printf("%d\n",ans);for(int i=1;i<=ans;i++)printf("%d %d\n",A[i],B[i]);
    vector<int>Z;
    for(int i=1;i<=m;i++)if(!vis[i])Z.pb(i);
    while(Z.size()>=2){
        int x=Z.back();Z.pop_back();
        int y=Z.back();Z.pop_back();
        printf("%d %d\n",x,y);
    }
}
int main(){
    int T;scanf("%d",&T);
    while(T--)sol();
    return 0;
}