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

#define int long long

using pii=pair<int,int>;

const int N=1e5+1e3+7;

int T,n;

signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cin>>T;
    while(T--)
    {
        cin>>n;
        multiset<int> ms;
        map<int,vector<int> >v;
        for(int i=1;i<=n;i++)
        {
            int x,y;
            cin>>x>>y;
            v[x].push_back(y);
            ms.insert(y);
        }
        multiset<int> all;
        int ans=1e18;
        for(auto [x,ys]:v)
        {
            for(auto y:ys)
                ms.erase(ms.find(y));
            for(auto y:ys)
                all.insert(y);
            for(auto y:ys)
            {
                all.erase(all.find(y));
                if(!ms.size())
                {
                    auto it=all.lower_bound(x);
                    if(it!=all.end())
                        ans=min(ans,*it-x);
                    if(it!=all.begin())
                        ans=min(ans,x-*prev(it));
                }
                else
                {
                    if(*prev(ms.end())>=x)
                        ans=min(ans,*prev(ms.end())-x);
                    else
                    {
                        auto it=all.lower_bound(x);
                        if(it!=all.end())
                            ans=min(ans,*it-x);
                        if(it!=all.begin())
                            ans=min(ans,x-*prev(it));
                        ans=min(ans,x-*prev(ms.end()));
                    }
                }
                all.insert(y);
            }
        }
        cout<<ans<<"\n";
    }
}