#include <bits/stdc++.h>
using namespace std;

#define f first
#define s second
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define all(v) v.begin(), v.end()
#define sz(v) (int)v.size()
#define sq(a) ((a)*(a))

#define MOO(i,a,b) for (int i=a; i<b; i++)
#define M00(i,a) for (int i=0; i<a; i++)
#define MOOd(i,a,b) for (int i = (b)-1; i >= a; i--)
#define M00d(i,a) for (int i = (a)-1; i >= 0; i--)

#define per(i,a,b) for (int i = (b)-1; i >= a; i--)
#define rep(i,a,b) for (int i=a; i<b; i++)

#define FOR(i,a,b) for (int i=a; i<b; i++)
#define F0R(i,a) for (int i=0; i<a; i++)
#define ROF(i,a,b) for (int i = (b)-1; i >= a; i--)
#define R0F(i,a) for (int i = (a)-1; i >= 0; i--)

#define FAST ios::sync_with_stdio(0); cin.tie(0);
#define finish(x) return cout << x << endl, 0;
#define dbg(x) cerr << ">>> " << #x << " = " << x << endl;
#define _ << " _ " <<

#define int long long

template<class T> bool ckmin(T&a, T&b) { bool B = a > b; a = min(a,b); return B; }
template<class T> bool ckmax(T&a, T&b) { bool B = a < b; a = max(a,b); return B; }

typedef long double ld;
typedef pair<int,int> pi;
typedef pair<ld,ld> pld;
typedef complex<ld> cd;

typedef vector<int> vi;
typedef vector<ld> vld;
typedef vector<vector<int>> vvi;

const ld PI = acos(-1.0);
const ld EPS = 1e-7;
const int MOD = 1e9+7;

// Really should be changed to a modular int class 
int POW(int b, int e) {
	int r = 1;
	while(e) {
		if(e % 2 == 1) {
			r *= b;
			r %= MOD;
		}
		e /= 2;
		b *= b;
		b %= MOD;
	}
	return r;
}
int INV(int a) {
	return POW(a, MOD-2);
}
//Constants and Variables here
void solve() {
	int n; cin >> n;
	vector<pi> price(n);
	M00(i, n) {
		int a, b;
		cin >> a >> b;
		price[i] = mp(a,b);
	}
	sort(all(price));
	int l = 0;
	int r = n-1;
	int money = 0;
	while(l < r) {
		int q = min(price[r].s, price[l].s);
		money += (price[r].f - price[l].f) * q; 
		price[r].s -= q;
		price[l].s -= q;
		if(price[r].s == 0) r--;
		if(price[l].s == 0) l--;
	}
	cout << money << endl;

}

int32_t main() { FAST
	mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
	int t; cin >> t;
	while(t--) solve();	
}