#include <bits/stdc++.h>
using namespace std;
const int dr[]{-1, -1, 0, 1, 1, 1, 0, -1};
const int dc[]{0, 1, 1, 1, 0, -1, -1, -1};
void run() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
}
void solve() {
  int n, m;
  cin >> n >> m;
  vector<pair<int, int>> v(m);
  vector<int> id;
  for (auto &it : v) {
    cin >> it.first >> it.second;
    id.push_back(it.first);
  }
  sort(id.rbegin(), id.rend());
  vector<long long> sum(1, 0);
  for (auto &it : id) sum.push_back(it + sum.back());
  long long mx = sum[min(n, m)];
  for (auto &it : v) {
    int tmp_n = n;
    int j = upper_bound(id.begin(), id.end(), it.second, greater<int>()) -
            id.begin();
    long long cur = 0;
    if (it.first < it.second) {
      cur += it.first;
      tmp_n--;
    }
    j = min(j, tmp_n);
    cur += sum[j];
    tmp_n -= j;
    cur += 1LL * tmp_n * it.second;
    mx = max(mx, cur);
  }
  cout << mx << "\n";
}
int main() {
  run();
  int T;
  cin >> T;
  while (T--) {
    solve();
  }
}
