#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  int t;
  cin >> t;
  while (t--) {
    long long n, m;
    cin >> n >> m;
    vector<pair<long long, long long>> ar(m);
    for (int i = 0; i < m; ++i) {
      cin >> ar[i].first >> ar[i].second;
    }
    sort(ar.begin(), ar.end());
    vector<long long> psa(m + 1);
    for (int i = 1; i < m + 1; ++i) {
      psa[i] = psa[i - 1] + ar[i - 1].first;
    }
    long long ans = 0;
    for (int i = 0; i < m; ++i) {
      long long a = ar[i].first;
      long long b = ar[i].second;
      int j = lower_bound(ar.begin(), ar.end(), make_pair(b, LLONG_MAX)) -
              ar.begin();
      long long cur = 0;
      if (m - j <= n) {
        cur += psa[m] - psa[j];
        int x = n - (m - j);
        cur += a + (x - 1) * b;
        if (j <= i) {
          cur -= a;
          cur += b;
        }
      } else {
        cur += psa[m] - psa[m - n];
      }
      ans = max(ans, cur);
    }
    cout << ans << '\n';
  }
  return 0;
}
