#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 998244353;
// constexpr int MOD = 1000000007;
constexpr int DY4[]{1, 0, -1, 0}, DX4[]{0, -1, 0, 1};
constexpr int DY8[]{1, 1, 0, -1, -1, -1, 0, 1};
constexpr int DX8[]{0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U>
inline bool chmax(T& a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U>
inline bool chmin(T& a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

void solve() {
  int n, l; cin >> n >> l;
  vector<int> x(n), y(n); REP(i, n) cin >> x[i] >> y[i];
  const int k = llround(sqrt(n)), len = (l + 1 + k - 1) / k;
  vector<vector<int>> block(k);
  REP(i, n) block[y[i] / len].push_back(i);
  REP(i, k) {
    if (i % 2 == 0) {
      ranges::sort(block[i], {}, [&](const int i) -> int { return x[i]; });
    } else {
      ranges::sort(block[i], greater<int>(), [&](const int i) -> int { return x[i]; });
    }
  }
  vector<int> ans;
  REP(i, k) for (const int j : block[i]) ans.emplace_back(j);
  cout << n << '\n';
  for (const int id : ans) cout << x[id] << ' ' << y[id] << '\n';
}

int main() {
  int t; cin >> t;
  while (t--) solve();
  return 0;
}