#include <algorithm>
#include <array>
#include <iostream>
#include <vector>

using namespace std;

const int MOD = 998244353;
void solve() {
  int n;
  cin >> n;
  vector<array<int, 2>> v(n);
  for(auto& x: v) {
    cin >> x[0] >> x[1];
    if(x[0] > x[1]) swap(x[0], x[1]);
  }
  sort(v.begin(), v.end(), [&](auto a, auto b) -> bool {
    return a[0] * int64_t(a[1]) < b[0] * int64_t(b[1]);
  });
  int64_t ret = 1;
  for(int i = 0; i + 1 < n; i++) {
    if(v[i][0] > v[i+1][0] || v[i][1] > v[i+1][1]) return void(cout << "0\n");
  }
  for(int i = 0; i < n;) {
    int j = i+1;
    while(j < n && v[i] == v[j]) j++;
    for(int a = 2; a <= j-i; a++) {
      ret *= a;
      ret %= MOD;
    }
    i = j;
  }
  v.erase(unique(v.begin(), v.end()), v.end());
  for(int i = 0; i + 1 < v.size(); i++) {
    int64_t inc1 = 1;
    inc1 *= v[i+1][0] - v[i][0] + 1;
    inc1 %= MOD;
    inc1 *= v[i+1][1] - v[i][1] + 1;
    inc1 %= MOD;
    if(v[i][0] != v[i][1]) {
      if(v[i+1][0] >= v[i][1] && v[i+1][1] >= v[i][0]) {
        int64_t inc2 = 1;
        inc2 *= v[i+1][0] - v[i][1] + 1;
        inc2 %= MOD;
        inc2 *= v[i+1][1] - v[i][0] + 1;
        inc2 %= MOD;
        inc1 += inc2;
        inc1 %= MOD;
      }
    }
    ret *= inc1;
    ret %= MOD;
  }
  if(v.back()[0] != v.back()[1]) {
    ret *= 2;
    ret %= MOD;
  }
  cout << ret << "\n";
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  int t;
  cin >> t;
  while(t--) solve();
}