#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<PII> v;
	for (int i = 1; i <= n; i++)
	{
		int k; cin >> k;
		for (int j = 1; j <= k; j++)
		{
			int x; cin >> x;
			v.pb({x, i});
		}
	}
	//exit(0);
	sort(v.begin(), v.end());
	
	//for (auto it : v) cout << it.fi << ' ' << it.se << endl;
	
	if (n == 1)
	{
		cout << 0 << endl;
		return;
	}
	map<int, int> q;
	int kind = 0;
	int ans = 1e17;
	//cout << endl;
	int r = 0;
	int ma = 0;
	for (int l = 0; l < v.size() - n + 1; l++)
	{
		int c = v[l].fi, ver = v[l].se;
		if (kind == n) 
		{
			//cout << ver << ' ' << ver1 << endl;
			//cout << c << ' ' << ma << endl;
			ans = min(ma - c, ans);
		}
		while (kind != n && r < v.size())
		{
			int c1 = v[r].fi, ver1 = v[r].se;
			if (q[ver1] != 0) q[ver1]++, r++;
			else
			{
				q[ver1]++; kind++;
				r++;
				ma = c1;
			}
			if (kind == n) 
			{
				//cout << ver << ' ' << ver1 << endl;
				//cout << c << ' ' << ma << endl;
				ans = min(ma - c, ans);
				break;
			}
		}
		
		//cout << q[3] << endl;
		// q[ver]++;
		// if (q[ver] == 1) kind++;
		
		//if (kind == n) ans = min(ma - c, ans);
		
		q[ver]--;
		//if (ver == 3) cout << q[ver] << "!!!!" << endl;
		if (q[ver] == 0) kind--;
		
	}
	cout << ans << endl;
} 

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