#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using pr = pair<int, int>;
using prll = pair<long, long>;
using V = vector<int>;
using Vll = vector<long long>;
template <typename T, typename TT>
pr operator+(pair<T, TT> a, pair<T, TT> b) {
  return {a.first + b.first, a.second + b.second};
}
template <typename T, typename TT>
ostream& operator<<(ostream& s, pair<T, TT> t) {
  return s << "(" << t.first << "," << t.second << ")";
}
template <typename T>
ostream& operator<<(ostream& s, vector<T> t) {
  for (auto itr : t) s << itr << " ";
  return s;
}
int n, m;
vector<pair<int, int>> a(200000);
vector<long long> c(100000);
int binSearch(int x) {
  int beg = 0;
  int last = m - 1;
  while (beg < last) {
    int mid = beg + (last - beg + 1) / 2;
    if (a[mid].first < x)
      last = mid - 1;
    else
      beg = mid;
  }
  if (a[beg].first < x) return -1;
  return beg;
}
bool cmp(pr a, pr b) {
  if (a.first == b.first) return a.second > b.second;
  return a.first > b.first;
}
int main() {
  ios_base::sync_with_stdio(NULL);
  cin.tie(0);
  cout.tie(0);
  int T;
  cin >> T;
  while (T--) {
    cin >> n >> m;
    for (int i = 0; i < int(m); i++) {
      int x, y;
      cin >> x >> y;
      a[i] = {x, y};
    }
    sort(a.begin(), a.begin() + m, cmp);
    c[0] = a[0].first;
    for (int i = 0; i < int(m - 1); i++) c[i + 1] = c[i] + a[i + 1].first;
    ll ans = INT_MIN;
    ans = c[min(n, m) - 1];
    for (int i = 0; i < int(m); i++) {
      int beg = binSearch(a[i].second);
      int t = min(beg, n - 3);
      if (beg >= i) t = min(beg, n - 2);
      if (t < 0)
        ans = max(ans, a[i].first + (n - 1) * 1LL * a[i].second);
      else if (t >= i)
        ans = max(ans, c[t] + (n - t - 1) * 1LL * a[i].second);
      else
        ans = max(ans, c[t] + (n - t - 2) * 1LL * a[i].second + a[i].first);
    }
    cout << ans << "\n";
  }
  return 0;
}
