#include <iostream>
#include <vector>
#include <queue>
#include <cassert>
#include <climits>

#define X 55

using namespace std;

void solve();
int counter;
int dist(pair <int, int> a, pair <int, int> b);

class E
{
public:
    int start, end, val;
    E(int x, int y, int z)
    {
        start = x;
        end = y;
        val = z;
    }

    friend bool operator < (const E& A, const E& B)
    {
        return A.val < B.val;
    }
};

int main()
{
    int T;
    cin >> T;
    while(T--)
        solve();
}

void solve()
{
    int N;
    cin >> N;
    vector <vector <pair <int, int> > > coord;
    for(int i=1; i<=N; i++)
    {
        int P;
        cin >> P;
        vector <pair <int, int> > temp;
        for(int j=0; j<P; j++)
        {
            int temp0, temp1;
            cin >> temp0 >> temp1;
            temp.push_back(make_pair(temp0, temp1));
        }
        coord.push_back(temp);
    }

    int A[N][N];
    for(int i=0; i<N; i++)
        A[i][i] = 0;
    int counter = 0;
    priority_queue <E> B;
    for(int i=0; i<N; i++)
        for(int j=0; j<N; j++)
            A[i][j] = INT_MAX;

    for(int i=0; i<N; i++)
        for(int j=i+1; j<N; j++)
        {
            int tempAns = INT_MAX;
            for(int I=0; I<coord[i].size(); I++)
                for(int J=0; J<coord[j].size(); J++)
                    tempAns = min(tempAns, dist(coord[i][I], coord[j][J]));
            A[i][j] = tempAns;
        }

    for(int i=0; i<N; i++)
        for(int j=i+1; j<N; j++)
            A[j][i] = A[i][j];

    /*
    for(int i=0; i<N; i++)
    {
        for(int j=0; j<N; j++)
            cout << A[i][j] << "\t";
        cout << endl;
    }
    */

    int head = 0;
    int ans;
    bool flag[N];
    for(int i=0; i<N; i++)
        flag[i] = true;
    flag[0] = false;

    while(++counter && counter < N)
    {
        for(int i=0; i<N; i++)
            if(flag[i])
                B.push(E(head, i, A[head][i]));

        while(!flag[B.top().end] && !B.empty())
            B.pop();
        if(B.empty()) assert(0);
        ans = B.top().val;
        head = B.top().end;
        flag[head] = false;
        B.pop();
    }
    cout << (ans)/2 << endl;
}


int dist(pair <int, int> a, pair <int, int> b)
{
    return max(abs(a.first - b.first), abs(a.second - b.second));
}