#pragma GCC optimize("O2")
#include <algorithm>
#include <array>
#include <bit>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cfenv>
#include <cfloat>
#include <chrono>
#include <cinttypes>
#include <climits>
#include <cmath>
#include <compare>
#include <complex>
#include <concepts>
#include <cstdarg>
#include <cstddef>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <deque>
#include <fstream>
#include <functional>
#include <initializer_list>
#include <iomanip>
#include <ios>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <map>
#include <memory>
#include <new>
#include <numbers>
#include <numeric>
#include <ostream>
#include <queue>
#include <random>
#include <ranges>
#include <set>
#include <span>
#include <sstream>
#include <stack>
#include <streambuf>
#include <string>
#include <tuple>
#include <type_traits>
#include <variant>

#define int ll
#define INT128_MAX (__int128)(((unsigned __int128) 1 << ((sizeof(__int128) * __CHAR_BIT__) - 1)) - 1)
#define INT128_MIN (-INT128_MAX - 1)

#define clock chrono::steady_clock::now().time_since_epoch().count()

#ifdef DEBUG
#define dbg(x) cout << (#x) << " = " << x << '\n'
#else
#define dbg(x)
#endif

namespace R = std::ranges;
namespace V = std::views;

using namespace std;

using ll = long long;
using ull = unsigned long long;
using ldb = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
//#define double ldb

template<class T>
ostream& operator<<(ostream& os, const pair<T, T> pr) {
  return os << pr.first << ' ' << pr.second;
}
template<class T, size_t N>
ostream& operator<<(ostream& os, const array<T, N> &arr) {
  for(const T &X : arr)
    os << X << ' ';
  return os;
}
template<class T>
ostream& operator<<(ostream& os, const vector<T> &vec) {
  for(const T &X : vec)
    os << X << ' ';
  return os;
}
template<class T>
ostream& operator<<(ostream& os, const set<T> &s) {
  for(const T &x : s)
    os << x << ' ';
  return os;
}

using lld = int64_t;

class DSU {
	vector<int> v;
public:
	DSU(int n): v(n) { iota(v.begin(), v.end(), 0); }
	int query(int u) { return v[u] == u ? u : v[u] = query(v[u]); }
	void merge(int x, int y) { v[query(x)] = query(y); }
};

template <typename T>
struct Point {
	T x, y;
	Point(T x_ = 0, T y_ = 0): x(x_), y(y_) {}
	Point operator-(const Point &rhs) const {
		return Point(x - rhs.x, y - rhs.y);
	}
};

typedef Point<int> P;
vector<tuple<int, int, int>> manhattanMST(vector<P> ps) {
	vector<int> id(ps.size());
	iota(id.begin(), id.end(), 0);
	vector<tuple<int, int, int>> edges;
	for (int k = 0; k < 4; ++k) {
		sort(id.begin(), id.end(), [&](int i, int j) {
			return (ps[i] - ps[j]).x < (ps[j] - ps[i]).y;
		});
		map<int, int> sweep;
		for (int i : id) {
			for (auto it = sweep.lower_bound(-ps[i].y);
					 it != sweep.end(); sweep.erase(it++)) {
				int j = it->second;
				P d = ps[i] - ps[j];
				if (d.y > d.x) break;
				edges.emplace_back(d.y + d.x, i, j);
			}
			sweep[-ps[i].y] = i;
		}
		for (P &p : ps)
			if (k & 1) p.x = -p.x;
			else swap(p.x, p.y);
	}
	return edges;
}

vector<int> MST(int n, const vector<tuple<int, int, int>> &e) {
	vector<int> idx(e.size());
	iota(idx.begin(), idx.end(), 0);
	sort(idx.begin(), idx.end(), [&](int i, int j){
		return get<0>(e[i]) < get<0>(e[j]);
	});
	vector<int> r;
	DSU dsu(n);
	for (int o: idx) {
		const auto &[w, i, j] = e[o];
		if (dsu.query(i) == dsu.query(j))
			continue;
		r.push_back(o);
		dsu.merge(i, j);
	}
	return r;
}

signed main() {
	ios_base::sync_with_stdio(false);
	cin.tie(nullptr);

  int t; cin >> t;
  while(t--) {
    int n, l; cin >> n >> l;
    vector<P> ps(n);
    for(auto &[x, y] : ps)
      cin >> x >> y;

    auto e = manhattanMST(ps);
    auto r = MST(n, e);
    vector<vector<int>> g(n);
    for(auto i : r) {
      auto [_, u, v] = e[i];
      g[u].emplace_back(v);
      g[v].emplace_back(u);
    }

    vector<P> ans;
    auto dfs = [&](int v, int p, auto self) -> void {
      ans.emplace_back(ps[v]);
      for(int x : g[v]) {
        if (x == p) continue;
        self(x, v, self);
        ans.emplace_back(ps[v]);
      }
    };

    dfs(0, -1, dfs);

    cout << ssize(ans) << '\n';
    for(auto [x, y] : ans)
      cout << x << ' ' << y << '\n';
  }

	return 0;
}