#include <bits/stdc++.h>
#define sz(x) ((int)(x).size())
#define all(x) begin(x), end(x)
#ifdef memset0
#define log(...) fprintf(stderr, __VA_ARGS__)
#else
#define endl '\n'
#define log(...) (void(0))
#endif
using namespace std;
using ll = long long;
using lf = long double;
using ull = unsigned long long;
using pll = pair<ll, ll>;

const int N = 200011;
const ll INF = 4e18;
pll a[N];
multiset<ll> S;
int main() {
#ifdef memset0
  freopen("E.in", "r", stdin);
#endif
  cin.tie(0)->sync_with_stdio(0);
  int task;
  cin >> task;
  while (task--) {
    S.clear();
    S.insert(-INF), S.insert(INF);
    int n;
    cin >> n;
    for (int i = 1; i <= n; ++i) cin >> a[i].first >> a[i].second, S.insert(a[i].second);
    sort(a + 1, a + n + 1);
    ll ans = 4e18, v = -INF;
    for (int i = n; i; --i) {
      S.erase(S.find(a[i].second));
      auto it = S.lower_bound(a[i].first);
      if (i < n) ans = min(ans, abs(v - a[i].first));
      ll nxt = max(*it, v);
      ll pre = max(*--it, v);
      ans = min(ans, min(abs(nxt - a[i].first), abs(a[i].first - pre)));
      v = max(v, a[i].second);
    }
    cout << ans << '\n';
  }
  return 0;
}