#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N=1e5+5;
#define F first
#define S second
pair<ll,ll> a[N];
ll suf[N];
int T,n;
multiset<ll> s;
int main(){
    for (cin>>T; T; T--){
        scanf("%d",&n);
        for (int i=1; i<=n; i++) scanf("%lld%lld",&a[i].F,&a[i].S);
        sort(a+1,a+1+n); ll ans=2e18;
        for (int i=n; i>=1; i--) suf[i]=max(i==n?0ll:suf[i+1],a[i].S);
        for (int i=1; i<=n; i++){
            if (suf[i+1]>=a[i].F){ ans=min(ans,suf[i+1]-a[i].F); continue; }
            auto it=s.lower_bound(a[i].F);
            if (it!=s.end())
                ans=min(ans,abs((*it)-a[i].F));
            if (it!=s.begin()){
                it--;
                ans=min(ans,abs(max(suf[i+1],(*it))-a[i].F));
            }
            s.insert(a[i].S);
        }
        for (int i=1; i<=n; i++) suf[i]=0;
        printf("%lld\n",ans); s.clear();
    }
}
/*
1
3
3 5
4 7
6 2
*/