#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int N, L;
int X[201010], Y[201010], ord[201010];
void solve(){
    cin >> N >> L;
    for(int i = 0;i < N;i++)cin >> X[i] >> Y[i];
    for(int i = 0;i < N;i++)ord[i] = i;
    int B = L / sqrt(N);
    B = max(1, B);
    sort(ord, ord + N, [&B](int a, int b){
        if(X[a] / B == X[b] / B){
            return ((X[a] / B) & 1) ? Y[a] > Y[b] : Y[a] < Y[b];
        }
        return X[a] / B < X[b] / B;
    });
    cout << N << "\n";
    for(int i = 0;i < N;i++){
        cout << X[ord[i]] << " " << Y[ord[i]] << "\n";
    }
}
int main(void){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    
    int t; cin >> t;
    while(t--)solve();
    return 0;
}