#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using db = double;
using ld = long double;
template <typename T>
using V = vector<T>;
template <typename T>
using VV = vector<vector<T>>;
constexpr ll mod = 1000000007;
constexpr ll INF = 1000000099;
constexpr ll LINF = (ll)(1e18 + 99);
const vector<ll> dx = {-1, 1, 0, 0}, dy = {0, 0, -1, 1};
template <typename T, typename U>
inline bool chmin(T& t, const U& u) {
  if (t > u) {
    t = u;
    return 1;
  }
  return 0;
}
template <typename T, typename U>
inline bool chmax(T& t, const U& u) {
  if (t < u) {
    t = u;
    return 1;
  }
  return 0;
}
template <typename T>
inline T gcd(T a, T b) {
  return b ? gcd(b, a % b) : a;
}
template <typename T, typename Y>
inline T mpow(T a, Y n) {
  T res = 1;
  for (; n; n >>= 1) {
    if (n & 1) res = res * a;
    a = a * a;
  }
  return res;
}
signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(20);
  int qq;
  cin >> qq;
  while (qq--) {
    int n;
    cin >> n;
    V<ll> a(2 * n), b(2 * n), lim(n, n);
    for (ll i = 0; i < (ll)(n); ++i) {
      cin >> a[i] >> b[i];
      a[i + n] = a[i];
      b[i + n] = b[i];
    }
    ll ans = 0, res = LINF;
    for (ll i = 0; i < (ll)(n); ++i) {
      ans += max(0ll, a[i + 1] - b[i]);
    }
    for (ll i = 1; i < (ll)(n + 1); ++i) {
      if (a[i] - b[i - 1] <= 0) {
        chmin(res, a[i]);
      } else {
        chmin(res, b[i - 1]);
      }
    }
    cout << ans + res << '\n';
  }
}
