#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N=1e5+3;
int t,n,b[N],ans;
struct gg{
    int x,y;
}a[N];
set<int>s;
set<int>::iterator it;
bool cmp(gg a,gg b){
    if(a.x==b.x)return a.y<b.y;
    return a.x>b.x;
}
signed main(){
    b[0]=a[0].y=-3e18;
    scanf("%lld",&t);
    while(t--){
        scanf("%lld",&n);
        for(int i=1;i<=n;++i){
            scanf("%lld %lld",&a[i].x,&a[i].y);
        }
        sort(a+1,a+n+1,cmp);
        for(int i=1;i<=n;++i){
            b[i]=max(b[i-1],a[i-1].y);
        }
        s.clear();
        s.insert(-3e18);
        s.insert(3e18);
        ans=6e18;
        for(int i=n;i;--i){
            it=s.lower_bound(a[i].x);
            --it;
            if(abs(b[i]-a[i].x)>abs(*it-a[i].x)&&(*it)>b[i])b[i]=*it;
            ++it;
            if(abs(b[i]-a[i].x)>abs(*it-a[i].x)&&(*it)>b[i])b[i]=*it;
            ans=min(ans,abs(b[i]-a[i].x));
            s.insert(a[i].y);
        }
        cout<<ans<<endl;
    }
}