#include <bits/stdc++.h>
#define int int64_t

using namespace std;
deque <int> a, b, c;

int get(int l, int r){
    if(r < l) return 0LL;
    if(l == 0) return c[r];
    else return c[r] - c[l - 1];
}


int32_t main()
{
    int t;
    cin >> t;
    while (t--)
    {
        int n;
        cin >> n;
        a.resize(n);
        b.resize(n);
        c.resize(n);
        for (int i = 0; i < n; i++)
            cin >> a [i] >> b [i];
        for (int i = 0; i < n; i++)
        {
            if (i == n - 1)
                c [0] = max(a [0] - b [i], 0LL);
            else
                c [i + 1] = max(a [i + 1] -  b [i], 0LL);
        }
        for (int i = 1; i < n; i++)
            c [i] += c [i - 1];
        int ans = LLONG_MAX;
        for (int i = 0; i < n; i++)
        {
            int cnt = a [i] + get(0, i - 1) + get(i + 1, n - 1);
            ans = min(ans, cnt);
        }
        cout << ans << "\n";
    }
}