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

const int MAXN = 200005;
typedef long long ll;
typedef pair<ll, ll> PR;
#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 --) {
		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, [&](PR a, PR b){ return (a.fi > b.fi) || (a.fi == b.fi && a.se < b.se); });
		ll ans = (ll)2e18;
		Set.clear(), mx[0] = -(ll)2e18;
		for (int i = 1; i <= n ; ++ i) mx[i] = max(mx[i - 1], a[i].se);
		for (int i = n; i >= 1 ; -- i) {
			if (mx[i - 1] >= a[i].fi) ans = min(ans, mx[i - 1] - a[i].fi);
			else {
				ll t = mx[i - 1];
				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(t - a[i].fi));
			}
			Set.insert(a[i].se);
		}

		Set.clear();
		sort(a + 1, a + n + 1, [&](PR a, PR b){ return (a.fi > b.fi) || (a.fi == b.fi && a.se > b.se); });
		for (int i = 1; i <= n ; ++ i) mx[i] = max(mx[i - 1], a[i].se);
		for (int i = n; i >= 1 ; -- i) {
			if (mx[i - 1] >= a[i].fi) ans = min(ans, mx[i - 1] - a[i].fi);
			else {
				ll t = mx[i - 1];
				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(t - a[i].fi));
			}
			Set.insert(a[i].se);
		}
		printf("%lld\n", ans);
	}
	return 0;
}