#include <bits/stdc++.h>
#include <cstdio>
#define int long long
#define PII pair<int, int>
#pragma GCC optimize("Ofast")
#define NO {puts("No") ; return ;}
#define YES {puts("Yes") ; return ;}
#define pb push_back
#define endl "\n"
#define fi first
#define se second
#define IOS std::ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
using namespace std;
mt19937 rd(time(0));
const int N = 1e5 + 10;

void solve() {
	int n; cin >> n;
	vector<vector<int>> a(n);

	for (int i = 0; i < n; i ++ ) {
		int m; cin >> m;
		for (int j = 0; j < m; j ++ ) {
			int x; cin >> x;
			a[i].pb(x);
		}
		sort(a[i].begin(), a[i].end());
	}

	if (n == 1) {
		cout << 0 << endl;
		return ;
	}

	int ans = LONG_LONG_MAX;

	for (int i = 0; i < a[0].size(); i ++ ) {
		int c = a[0][i];
		vector<int> b, d, e, f;
		b.pb(c);
		d.pb(c);
		e.pb(c);
		f.pb(c);
		for (int j = 1; j < n; j ++ ) {
			int l = -1, r = a[j].size();
			while (l + 1 != r) {
				int mid = l + r >> 1;
				if (a[j][mid] >= c) r = mid;
				else l = mid;
			}			
			
			int ll = -1, rr = a[j].size();
			while (ll + 1 != rr) {
				int mid = ll + rr >> 1;
				if (a[j][mid] <= c) ll = mid;
				else rr = mid;
			}
			
			if (r != a[j].size() && ll != -1) {				
				if (abs(c - a[j][r]) != abs(c - a[j][ll])) {
					if (abs(c - a[j][r]) > abs(c - a[j][ll]))
						b.pb(a[j][ll]), d.pb(a[j][ll]);
					else
						b.pb(a[j][r]), d.pb(a[j][r]);	
				} else {
					b.pb(a[j][ll]);
					d.pb(a[j][r]);
				}
				e.pb(a[j][ll]);
				f.pb(a[j][r]);
					
			} else if (r != a[j].size()) {
				b.pb(a[j][r]);
				d.pb(a[j][r]);
				f.pb(a[j][r]);
				e.pb(a[j][r]);
			} else if (ll != -1) {
				b.pb(a[j][ll]);
				d.pb(a[j][ll]);		
				e.pb(a[j][ll]);	
				f.pb(a[j][ll]);			
			}
		}
	
		sort(b.begin(), b.end());	
		sort(d.begin(), d.end());	
		sort(e.begin(), e.end());	
		sort(f.begin(), f.end());	
		ans = min(min(ans, e.back() - e[0]), f.back() - f[0]);
		ans = min(min(ans, d.back() - d[0]), b.back() - b[0]);
	}
	cout << ans << endl;
	
} 

signed main() {
    IOS;
    int t; cin >> t;
    while (t -- ) 
    solve();
    
    return 0;
}