#include <bits/stdc++.h>
using namespace std;

#define all(x) begin(x), end(x)
#ifdef CKISEKI
#define safe cerr << __PRETTY_FUNCTION__ << " line " << __LINE__ << " safe\n"
#define debug(a...) debug_(#a, a)
#define orange(a...) orange_(#a, a)
template <typename ...T>
void debug_(const char *s, T ...a) {
    cerr << "\e[1;32m(" << s << ") = (";
    int cnt = sizeof...(T);
    (..., (cerr << a << (--cnt ? ", " : ")\e[0m\n")));
}
template <typename I>
void orange_(const char *s, I L, I R) {
    cerr << "\e[1;32m[ " << s << " ] = [ ";
    for (int f = 0; L != R; L++)
        cerr << (f++ ? ", " : "") << *L;
    cerr << " ]\e[0m\n";
}
#else 
#define safe ((void)0)
#define debug(...) safe
#define orange(...) safe
#endif

int main() {
    cin.tie(nullptr)->sync_with_stdio(false);
    int t;
    cin >> t;
    while (t--) {
        int n;
        cin >> n;
        multiset<int64_t> aval, must;
        map<int64_t, vector<int64_t>> a;
        for (int i = 0; i < n; ++i) {
            int64_t x, y;
            cin >> x >> y;
            a[x].push_back(y);
            aval.insert(y);
        }
        int64_t ans = numeric_limits<int64_t>::max();
        for (auto it = a.rbegin(); it != a.rend(); ++it) {
            multiset<int64_t> cur;
            int64_t x = it->first;
            for (auto y : it->second) {
                cur.insert(y);
                aval.erase(aval.find(y));
            }

            auto upd = [x, &ans](const multiset<int64_t> &s) {
                auto it = s.lower_bound(x);
                if (it != s.end()) {
                    ans = min(ans, *it - x);
                }
                if (it != s.begin()) {
                    ans = min(ans, x - *prev(it));
                }
            };
            
            for (auto y : it->second) {
                cur.erase(cur.find(y));
                if (not must.empty() and *must.rbegin() >= x) {
                    ans = min(ans, *must.rbegin() - x);
                } else {
                    upd(must);
                    upd(cur);
                    upd(aval);
                }
                cur.insert(y);
            }

            for (auto y : cur)
                must.insert(y);
        }
        cout << ans << '\n';
    }
    return 0;
}