import math
import os
import random
import re
import sys
from math import gcd
from math import sqrt
from collections import Counter\
for _ in range(int(input())):
n = int(input())
x = 1000000000000000
y = 0
for i in range(n):
l,r = list(map(int,input().split()))
y = max(l,y)
x = min(r,x)
print(max(y-x,0))#include <bits/stdc++.h>
#define ll long long
#define unl unsigned long long
#define all(v,s,e) v.begin()+s,v.end()-e
using namespace std;
int MOD=1e9+7;
signed main(){
int tc; cin>>tc;
while (tc--){
int n; cin>>n;
vector<pair<ll,ll>>a;
for (int i = 0; i < n; ++i) {
ll u,v; cin>>u>>v;
a.push_back({u,v});
}
sort(a.rbegin(),a.rend());
ll x=a[0].first,y=1e10;
for (int i = 1; i < n; ++i) {
y=min(y,a[i].second);
}
if(x<=y)cout<<0;
else cout<<x-y;
cout<<'\n';
}
return 0ll;
}
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