#include <bits/stdc++.h>
using namespace std;
int t;
long long b[3000000];
pair<long long, long long> a[3000000];
int main() {
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    for (int i = 0; i < n; ++i) {
      scanf("%lld%lld", &a[i].first, &a[i].second);
    }
    for (int i = 0; i < n; ++i) {
      b[(i + 1) % n] = a[(i + 1) % n].first - a[i].second;
    }
    long long ans = a[0].first, anw = 1e18;
    for (int i = 1; i < n; ++i) {
      if (b[i] > 0) {
        ans += b[i];
      }
    }
    anw = min(ans, anw);
    for (int i = 1; i < n; ++i) {
      ans -= a[i - 1].first;
      if (b[i] > 0) {
        ans -= b[i];
      }
      ans += a[i].first;
      if (b[i - 1] > 0) {
        ans += b[i - 1];
      }
      anw = min(ans, anw);
    }
    printf("%lld\n", anw);
  }
  return 0;
}
