#include<bits/stdc++.h>
using namespace std;
const int INF=0x3f3f3f3f;
#define endl '\n'
#define x first
#define y second
typedef long long ll;
typedef pair<int,int> PII;
PII a[100010];
int n,cnt=0;
void solve()
{
	
	
	scanf("%d",&n);
	for(int i=1;i<=n;i++) 
	{
		scanf("%d%d",&a[i].x,&a[i].y);	
		cnt+=a[i].y;
	}
	sort(a+1,a+n+1);
	int cnt1,cnt2;
	if(cnt&1)cnt1=(cnt-1)/2;
	else cnt1=cnt/=2;
	cnt2=cnt1;
	int cb=0,xs=0;


	for(int i=1;i<=n;i++)
	{
		cb+=a[i].x*min(a[i].y,cnt1);
		cnt1-=min(a[i].y,cnt1);
		if(cnt1<=0)break;
	}
	for(int i=n;i>=1;i--)
	{
		xs+=a[i].x*min(a[i].y,cnt2);
		cnt2-=min(a[i].y,cnt2);
		if(cnt2<=0)break;
	}
	printf("%d\n",xs-cb);
	//cout<<xs-cb<<endl;
}
/*
10 2
20 4
25 
30 7
50 1
*/
int main()
{
	//ios::sync_with_stdio(false);
	//ios::sync_with_stdio(0);cin.tie(0),cout.tie(0);
	int t;
	scanf("%d",&t);
	while(t--)
	{
		solve();
	}
	return 0;
}