#include <bits/stdc++.h>
using namespace std;
const long long INF = 1e18;
const int INFi = 2e9;
const int maxN = 1e5 + 5;
const int md = 998244353;
const int md2 = 1e9 + 7;
double getTime() { return clock() / (double)CLOCKS_PER_SEC; };
void solve() {
  int m, n;
  cin >> m >> n;
  vector<pair<int, int>> a(n);
  for (int i = 0; i < n; ++i) cin >> a[i].first >> a[i].second;
  sort((a).begin(), (a).end());
  vector<long long> suf(n + 1);
  suf[n] = 0;
  suf[n - 1] = a[n - 1].first;
  for (int i = n - 2; i >= 0; --i) suf[i] = suf[i + 1] + a[i].first;
  long long ans = 0;
  for (int i = 0; i < n; ++i) {
    long long res = 0;
    pair<int, int> kek = {a[i].second, -1};
    int l = lower_bound((a).begin(), (a).end(), kek) - a.begin();
    l = max(l, n - m);
    int cnt = n - l;
    res += suf[l];
    if (i < l && cnt < m) {
      cnt++;
      res += a[i].first;
    }
    res += 1ll * a[i].second * (m - cnt);
    ans = max(ans, res);
  }
  cout << ans << "\n";
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  int tests = 1;
  cin >> tests;
  for (int _ = 0; _ < tests; ++_) {
    solve();
  }
  return 0;
}
