#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <functional>
#include <iostream>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

using Int = long long;

template <class T1, class T2> ostream &operator<<(ostream &os, const pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> ostream &operator<<(ostream &os, const vector<T> &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; }
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << endl; }
template <class T> bool chmin(T &t, const T &f) { if (t > f) { t = f; return true; } return false; }
template <class T> bool chmax(T &t, const T &f) { if (t < f) { t = f; return true; } return false; }
#define COLOR(s) ("\x1b[" s "m")

////////////////////////////////////////////////////////////////////////////////
template <unsigned M_> struct ModInt {
  static constexpr unsigned M = M_;
  unsigned x;
  constexpr ModInt() : x(0U) {}
  constexpr ModInt(unsigned x_) : x(x_ % M) {}
  constexpr ModInt(unsigned long long x_) : x(x_ % M) {}
  constexpr ModInt(int x_) : x(((x_ %= static_cast<int>(M)) < 0) ? (x_ + static_cast<int>(M)) : x_) {}
  constexpr ModInt(long long x_) : x(((x_ %= static_cast<long long>(M)) < 0) ? (x_ + static_cast<long long>(M)) : x_) {}
  ModInt &operator+=(const ModInt &a) { x = ((x += a.x) >= M) ? (x - M) : x; return *this; }
  ModInt &operator-=(const ModInt &a) { x = ((x -= a.x) >= M) ? (x + M) : x; return *this; }
  ModInt &operator*=(const ModInt &a) { x = (static_cast<unsigned long long>(x) * a.x) % M; return *this; }
  ModInt &operator/=(const ModInt &a) { return (*this *= a.inv()); }
  ModInt pow(long long e) const {
    if (e < 0) return inv().pow(-e);
    ModInt a = *this, b = 1U; for (; e; e >>= 1) { if (e & 1) b *= a; a *= a; } return b;
  }
  ModInt inv() const {
    unsigned a = M, b = x; int y = 0, z = 1;
    for (; b; ) { const unsigned q = a / b; const unsigned c = a - q * b; a = b; b = c; const int w = y - static_cast<int>(q) * z; y = z; z = w; }
    assert(a == 1U); return ModInt(y);
  }
  ModInt operator+() const { return *this; }
  ModInt operator-() const { ModInt a; a.x = x ? (M - x) : 0U; return a; }
  ModInt operator+(const ModInt &a) const { return (ModInt(*this) += a); }
  ModInt operator-(const ModInt &a) const { return (ModInt(*this) -= a); }
  ModInt operator*(const ModInt &a) const { return (ModInt(*this) *= a); }
  ModInt operator/(const ModInt &a) const { return (ModInt(*this) /= a); }
  template <class T> friend ModInt operator+(T a, const ModInt &b) { return (ModInt(a) += b); }
  template <class T> friend ModInt operator-(T a, const ModInt &b) { return (ModInt(a) -= b); }
  template <class T> friend ModInt operator*(T a, const ModInt &b) { return (ModInt(a) *= b); }
  template <class T> friend ModInt operator/(T a, const ModInt &b) { return (ModInt(a) /= b); }
  explicit operator bool() const { return x; }
  bool operator==(const ModInt &a) const { return (x == a.x); }
  bool operator!=(const ModInt &a) const { return (x != a.x); }
  friend std::ostream &operator<<(std::ostream &os, const ModInt &a) { return os << a.x; }
};
////////////////////////////////////////////////////////////////////////////////

constexpr unsigned MO = 998244353;
using Mint = ModInt<MO>;


constexpr int INF = 1001001001;

int M;
vector<int> L, R;

int dp[4010][4010];

int main() {
  for (int numCases; ~scanf("%d", &numCases); ) { for (int caseId = 1; caseId <= numCases; ++caseId) {
    scanf("%*d%d", &M);
    L.resize(M);
    R.resize(M);
    for (int i = 0; i < M; ++i) {
      scanf("%d%d", &L[i], &R[i]);
      --L[i];
    }
    
    vector<int> xs;
    for (int i = 0; i < M; ++i) {
      xs.push_back(L[i]);
      xs.push_back(R[i]);
    }
    sort(xs.begin(), xs.end());
    xs.erase(unique(xs.begin(), xs.end()), xs.end());
    const int N = xs.size();
    for (int i = 0; i < M; ++i) {
      L[i] = lower_bound(xs.begin(), xs.end(), L[i]) - xs.begin();
      R[i] = lower_bound(xs.begin(), xs.end(), R[i]) - xs.begin();
    }
    
    vector<vector<int>> graph(N);
    for (int i = 0; i < M; ++i) {
      graph[R[i]].push_back(L[i]);
    }
    
    for (int k = 0; k <= N; ++k) {
      fill(dp[k], dp[k] + N, INF);
    }
    fill(dp[0], dp[0] + N, 0);
    for (int k = 0; ; ++k) {
      for (int u = N; --u >= 0; ) {
        if (u >= 1) {
          chmin(dp[k][u - 1], dp[k][u]);
        }
        for (const int v : graph[u]) {
          chmin(dp[k][v], dp[k][u] - 1);
        }
      }
// cerr<<"dp["<<k<<"] = ";pv(dp[k],dp[k]+N);
      if (k == N) break;
      for (int i = 0; i < M; ++i) {
        chmin(dp[k + 1][R[i]], dp[k][L[i]]);
      }
    }
    
    Int pmm = 1, qmm = 0;
    for (int u = 0; u < N; ++u) {
      Int pm = 0, qm = 1;
      for (int k = 1; k <= M; ++k) {
        Int p = -(dp[N][u] - dp[k][u]);
        Int q = N - k;
        if (pm * q < p * qm) {
          pm = p;
          qm = q;
        }
      }
      if (pmm * qm > pm * qmm) {
        pmm = pm;
        qmm = qm;
      }
    }
// cerr<<pmm<<"/"<<qmm<<endl;
    const Mint ans = Mint(pmm) / Mint(qmm);
    printf("%u\n", ans.x);
  }
#ifndef LOCAL
  break;
#endif
  }
  return 0;
}