#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <chrono>
#include <complex>
#include <cstring>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <unordered_map>
#include <vector>

using namespace std;

// BEGIN NO SAD
#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define trav(a, x) for(auto& a : x)
#define all(x) x.begin(), x.end()
#define sz(x) (int)(x).size()
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define lb lower_bound
#define ub upper_bound
typedef vector<int> vi;
#define f first
#define s second
#define derr if(0) cerr
void __print(int x) {cerr << x;}
void __print(long x) {cerr << x;}
void __print(long long x) {cerr << x;}
void __print(unsigned x) {cerr << x;}
void __print(unsigned long x) {cerr << x;}
void __print(unsigned long long x) {cerr << x;}
void __print(float x) {cerr << x;}
void __print(double x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}

template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ", "; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? ", " : ""), __print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
#define debug(x...) cerr << "\e[91m"<<__func__<<":"<<__LINE__<<" [" << #x << "] = ["; _print(x); cerr << "\e[39m" << flush;
// END NO SAD

template<class Fun>
class y_combinator_result {
  Fun fun_;
public:
  template<class T>
  explicit y_combinator_result(T &&fun): fun_(std::forward<T>(fun)) {}

  template<class ...Args>
  decltype(auto) operator()(Args &&...args) {
    return fun_(std::ref(*this), std::forward<Args>(args)...);
  }
};

template<class Fun>
decltype(auto) y_combinator(Fun &&fun) {
  return y_combinator_result<std::decay_t<Fun>>(std::forward<Fun>(fun));
}

template<class T>
bool updmin(T& a, T b) {
  if(b < a) {
    a = b;
    return true;
  }
  return false;
}
template<class T>
bool updmax(T& a, T b) {
  if(b > a) {
    a = b;
    return true;
  }
  return false;
}
typedef int64_t ll;

void rsolve() {
  int n, q;
  cin >> n >> q;
  vector<int> allv;
  vector<array<int, 2>> edges(q);
  auto valid = [&](ll thresh) -> bool {
    vector<ll> dp(n);
    for(int qq = 0; qq < sz(allv); qq++) {
      for(auto [a, b]: edges) {
        int aidx = lb(allv.begin(), allv.end(), a) - allv.begin();
        int bidx = lb(allv.begin(), allv.end(), b) - allv.begin();
        updmax(dp[bidx], dp[aidx] + 2);
        updmax(dp[aidx], dp[bidx] - thresh);
      }
      for(int i = 1; i < sz(dp); i++) updmax(dp[i], dp[i-1]);
    }
    for(auto [a, b]: edges) {
      int aidx = lb(allv.begin(), allv.end(), a) - allv.begin();
      int bidx = lb(allv.begin(), allv.end(), b) - allv.begin();
      if(updmax(dp[bidx], dp[aidx] + 2)) return false;
      if(updmax(dp[aidx], dp[bidx] - thresh)) return false;
      for(int i = 1; i < sz(dp); i++) if(updmax(dp[i], dp[i-1])) return false;
    }
    return true;
  };
  for(auto& x: edges) {
    cin >> x[0] >> x[1];
    x[0]--;
    assert(x[0] < x[1]);
    allv.pb(x[0]);
    allv.pb(x[1]);
  }
  sort(all(allv));
  allv.resize(unique(all(allv)) - allv.begin());
  ll lhs = 2;
  ll rhs = 10000;
  while(lhs < rhs) {
    int mid = (lhs+rhs)/2;
    if(valid(mid)) rhs = mid;
    else lhs = mid+1;
  }
  if(lhs%2 == 0) cout << (lhs/2) << "\n";
  else {
    cout << (lhs * (998244353+1)/2)%998244353 << "\n";
  }
}
void solve() {
  int t;
  cin >> t;
  while(t--) rsolve();
}

// what would chika do
// are there edge cases (N=1?)
// are array sizes proper (scaled by proper constant, for example 2* for koosaga tree)
// integer overflow?
// DS reset properly between test cases
// are you doing geometry in floating points
// are you not using modint when you should

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  solve();
}