#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long ti;
  cin >> ti;
  for (long long io = 0; io < ti; io++) {
    long long n, m;
    cin >> n >> m;
    vector<long long> a, ao, b;
    for (long long i = 0; i < m; i++) {
      long long x, y;
      cin >> x >> y;
      a.push_back(x);
      ao.push_back(x);
      b.push_back(y);
    }
    sort(a.begin(), a.end());
    long long sf[m + 1];
    long long sm = 0;
    for (long long i = m - 1; i >= 0; i--) {
      sm += a[i];
      sf[m - i] = sm;
    }
    long long ans = 0;
    if (n <= m) ans = sf[n];
    for (long long i = 0; i < m; i++) {
      long long v = b[i];
      long long idx = upper_bound(a.begin(), a.end(), v) - a.begin() + 1;
      long long avl = m - idx + 1;
      if (idx > m) {
        ans = max(ans, ao[i] + (n - 1) * b[i]);
      } else if (avl < n) {
        long long as = 0;
        as = as + sf[avl];
        long long rm = n - avl;
        if (ao[i] <= b[i]) {
          as += ao[i];
          rm--;
        }
        as += rm * b[i];
        ans = max(ans, as);
      }
    }
    cout << ans << endl;
  }
  return 0;
}
