#include <bits/stdc++.h>
using namespace std;
int n;
struct Pr
{
    long long x, y;
    bool operator < (const Pr& b)const
    {
        return y > b.y;
    }
}a[100005];
struct Unit
{
    long long x;
    int id;
    Unit(long long x = 0, int id = 0): x(x), id(id){}
    bool operator < (const Unit& b)const
    {
        return x < b.x || x == b.x && id < b.id;
    }
};
set<Unit> q;
void solve()
{
    scanf("%d", &n);
    for(int i = 0; i < n; i++)
        scanf("%lld%lld", &a[i].x, &a[i].y);
    sort(a, a + n);
    for(int i = 0; i < n; i++)
        q.insert(Unit(a[i].x, i));
    long long maxn = -1, minn = 0x7fffffffffffffff;
    for(int i = 0; i < n; i++){
        q.erase(Unit(a[i].x, i));
        if(i == n - 1){
            minn = min(minn, abs(maxn - a[i].y));
            continue;
        }
        auto p1 = q.lower_bound(Unit(a[i].y, -1));
        if(p1 != q.end() && p1->x > maxn)
            minn = min(minn, p1->x - a[i].y);
        if(p1 != q.begin()){
            p1--;
            if(p1->x > maxn)
                minn = min(minn,  a[i].y - p1->x);
        }
        if(i) minn = min(minn, abs(maxn - a[i].y));
        maxn = max(maxn, a[i].x);
    }
    printf("%lld\n", minn);
}
int main()
{
    int T;
    scanf("%d", &T);
    while(T--) solve();
    return 0;
}