#include <bits/stdc++.h>
using namespace std;
using i64 = long long;
int main() {
//	freopen("in.txt", "r", stdin);
	ios::sync_with_stdio(false), cin.tie(0);
	int T;
	for(cin >> T; T; T --) {
		int n;
		cin >> n;
		vector<pair<i64, i64>> a(n);
		for(auto &[x, y] : a) cin >> x >> y;
		sort(a.begin(), a.end());
		set<i64> s;
		vector<i64> mx(n);
		mx.back() = a.back().second;
		for(int i = n - 2; i >= 0; i --) mx[i] = max(mx[i + 1], a[i].second);
		i64 ans = 8e18;
		for(int i = 0; i < n - 1; i ++) {
			i64 cur = a[i].first;
			i64 val = mx[i + 1];
			if(val < cur) {
				auto it = s.upper_bound(cur);
				if(it != s.begin()) {
					it --;
					val = max(val, *it);
					ans = min(ans, abs(cur - val));
					it ++;
				} 
				if(it != s.end()) {
					val = max(val, *it);
					ans = min(ans, abs(cur - val));
				}
			} else {
				ans = min(ans, abs(cur - val));
			}
			s.insert(a[i].second);
		}
		cout << ans << '\n';
	}
	return 0;
}