#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  long long t, n, i, j, k, l, r, minn, maxx, ans, x, y;
  cin >> t;
  while (t--) {
    cin >> n;
    cin >> maxx >> minn;
    for (i = 1; i < n; i++) {
      cin >> x >> y;
      maxx = max(maxx, x);
      minn = min(minn, y);
    }
    if (maxx <= minn)
      ans = 0;
    else
      ans = maxx - minn;
    cout << ans << "\n";
  }
  return 0;
}
