#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;

int main(){
	int T, n;
	cin >> T;
	while(T--){
		cin >> n;
		unsigned long long ans = 0;
		vector<pair<int, unsigned long long> > store(n);
		int a;
		unsigned long long b;
		for(int i = 0; i < n; i++){
			cin >> a >> b;
			store[i] = make_pair(a, b);
		}
		sort(store.begin(), store.end());
		if(store[0].first == store[n-1].first){
			cout << 0 << endl;
			continue;
		}
		int l = 0, r = n - 1;
		while(l < r){
			unsigned long long temp = store[r].first - store[l].first;
			if(store[l].second >= store[r].second){
				ans += store[r].second * temp;
				store[l].second -= store[r].second;
				r--;
			}else{
				ans += store[l].second * temp;
				store[l].second = 0;
				store[r].second -= store[l].second;
			}
			if(!store[l].second)
			    l++;	    
		}
		cout << ans << endl;
	}
	return 0;
}