#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
void solve();
int main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int test_case;
  cin>>test_case;
  while (test_case--){
    solve();
  }
}
void solve(){
  int N,L;
  cin>>N>>L;
  vector P(N,array<int,2>());
  for(auto &i:P)cin>>i[0]>>i[1];
  sort(P.begin(),P.end());
  int sqN=sqrt(N)+1,sqL=L/sqN;
  vector dP(sqN+1,vector(0,array<int,2>()));
  for(int i=0;i<N;i++){
    dP[P[i][0]/sqL].push_back(P[i]);
  }
  for(auto &i:dP){
    sort(i.begin(),i.end());
  }
  vector ans(0,array<int,2>());
  for(int i=0;i<(int)dP.size();i++){
    if(i%2){
      reverse(dP[i].begin(),dP[i].end());
    }
    for(auto j:dP[i]){
      ans.push_back(j);
    }
  }
  cout<<ans.size()<<'\n';
  for(auto i:ans)cout<<i[0]<<' '<<i[1]<<'\n';
}