#include <bits/stdc++.h>
using namespace std;
const double pi = acos(-1.0);
int t;
long long sufa[100010];
long long a[100010];
pair<long long, long long> ab[100010];
long long n, m;
int main() {
  cin >> t;
  while (t--) {
    scanf("%lld %lld", &n, &m);
    for (long long i = 0; i < m; i++) {
      scanf("%lld %lld", &ab[i].first, &ab[i].second);
    }
    sort(ab, ab + m);
    sufa[m] = 0;
    sufa[m - 1] = a[m - 1] = ab[m - 1].first;
    for (int i = m - 1 - 1; i >= 0; i--) {
      a[i] = ab[i].first;
      sufa[i] = sufa[i + 1] + a[i];
    }
    long long ans = 0;
    if (n <= m) {
      ans = sufa[m - n];
    }
    for (long long i = 0; i < m; i++) {
      long long idx = lower_bound(a, a + m, ab[i].second) - a;
      idx = max(idx, m - n);
      long long costn = m - idx;
      long long costa = 0;
      if (idx > i && costn < n) {
        costa = ab[i].first;
        costn += 1;
      }
      ans = max(ans, sufa[idx] + costa + (n - costn) * ab[i].second);
    }
    printf("%lld\n", ans);
  }
  return 0;
}
