#pragma GCC optimize(3,"Ofast","inline")
#include<bits/stdc++.h>
#define ios ios::sync_with_stdio(0),cin.tie(0),cout.tie(0)
using namespace std;using ll = long long;using PLL = pair<ll,ll>;
const ll MAX = 1e18;const ll MIN = -1e18;const ll INF=0x3f3f3f3f;
const ll Q = 1e5+9;const ll MOD = 1e9 + 7;
vector<PLL> a;ll n;
bool cmp(PLL l,PLL r){
	if(l.first==r.first) return l.second<r.second;
	else return l.first<r.first;
}
struct cmp2
{
	bool operator()(PLL a,PLL b){
		return a.second>b.second;
	}
};

bool check(ll x){
	priority_queue<PLL,vector<PLL>,cmp2> q;
	for (ll i = 0; i < n; i++)
	{
		if(a[i].first<x) q.push({a[i]});
		else if(q.size() and a[i].first-(q.top().second-a[i].second)>=x) q.pop();
	}
	if(q.size()) return false;
	else return true;
}
void solve(){
   cin>>n;ll ma=MIN,mi=MAX;
	for (ll i = 0; i < n; i++)
	{
		ll o,p;cin>>o>>p;
		ma=max(ma,o);
		mi=min(mi,o);
		a.push_back({o,p});
	}
	sort(a.begin(),a.end(),cmp);
	ll l=mi,r=ma;ll ans=0;
	while(l<=r){
		ll mid=(l+r)/2;
		if(check(mid)) {
			l=mid+1;ans=mid;
		}else r=mid-1;
	}
	cout<<ans<<"\n";
}
int main(){
	ios;ll _=1;cin>>_;
	while (_--)solve();
	return 0;
}