#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define rep(i, n) for(int i=0;i<(n);++i)
#define rep1(i, n) for(int i=1;i<=(n);i++)
#define ll long long
using mint = modint998244353;
using P = pair<ll,ll>;
using lb = long double;
using T = tuple<ll, ll, ll>;
#ifdef LOCAL
#  include <debug_print.hpp>
#  define dbg(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#  define dbg(...) (static_cast<void>(0))
#endif

int main()
{
	// l * (l/m) + m * n <= 1000L
	// m = l/sqrt(n)
	int t;
	cin >> t;
	while(t--){
		int n, l;
		cin >> n >> l;
		vector<int> x(n), y(n);
		rep(i,n) cin >> x[i] >> y[i];
		int m = l/sqrt(n);
		vector<int> id;
		int M = l/m;
		vector<vector<int>> xs(M+1);
		rep(i,n){
			xs[y[i]/m].push_back(i);
		}
		rep(i,M+1) {
			if(i%2==0) sort(xs[i].begin(),xs[i].end(), [&](int a, int b){
				return x[a] < x[b];
			});
			else sort(xs[i].begin(),xs[i].end(), [&](int a, int b){
				return x[a]>x[b];
			});
		}
		rep(i,M+1) {
			for(int j : xs[i]) id.push_back(j);
		}
		cout << n << endl;
		ll ans = 0;
		rep(i,n){
			cout << x[id[i]] << " " << y[id[i]] << endl;
		}
		rep(i,n-1){
			ans += abs(x[id[i+1]]-x[id[i]]) + abs(y[id[i+1]]-y[id[i]]);
		}
		dbg(ans, 1000ll*l);

	}
	return 0;
}