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

const int MAXN = 200005;
typedef long long ll;
#define fi first
#define se second
#define PB push_back
#define MP make_pair

pair<ll, ll> a[MAXN];
set<ll> Set;
ll mx[MAXN];

signed main() {
#ifndef ONLINE_JUDGE
	freopen("a.in", "r", stdin);
#endif
	int Case;
	scanf("%d", &Case);
	while (Case --) {
		Set.clear();
		int n;
		scanf("%d", &n);
		for (int i = 1; i <= n ; ++ i) scanf("%lld%lld", &a[i].fi, &a[i].se);
		sort(a + 1, a + n + 1);
		reverse(a + 1, a + n + 1);
		ll ans = (ll)1e19;
		for (int i = 1; i <= n ; ++ i) mx[i] = max(mx[i - 1], a[i].se);
		for (int i = n; i >= 1 ; -- i) {
			ll t = -(ll)1e19;
			auto nxt = Set.lower_bound(a[i].fi), pre = nxt;
			if (pre != Set.begin()) {
				-- pre;
				if (abs(t - a[i].fi) > abs(*pre - a[i].fi)) t = *pre;
			}
			if (nxt != Set.end()) {
				if (abs(t - a[i].fi) > abs(*nxt - a[i].fi)) t = *nxt;
			}
			ans = min(ans, abs(max(mx[i - 1], t) - a[i].fi));
			Set.insert(a[i].se);
//			cout << a[i].fi << " " << mx[i - 1] << " " << t << endl;
		}
		printf("%lld\n", ans);
	}
	return 0;
}