#include <iostream>
#include <fstream>
#include <cmath>
#include <vector>
#include <ctime>
#include <cstdlib>
#include <iomanip>
using namespace std;

double sq(double x){ return x*x; }

class v3{
public:
  v3():x(0),y(0),z(0){}
  v3(double x,double y,double z):x(x),y(y),z(z){}

  double dist(const v3 &v){
    return sqrt(sq(x-v.x)+sq(y-v.y)+sq(z-v.z));
  }
  
  double x,y,z;
};

const double huge_num=1e6;

int main()
{
  srand(time(NULL));
  cout<<setiosflags(ios::fixed)<<setprecision(10);
  ifstream cin("balls.in");
  int cases;cin>>cases;
  while(cases--){
    int n;cin>>n;
    vector<v3> cs(n);
    vector<double> rs(n);
    for (int i=0;i<n;i++){
      double x,y,z;cin>>x>>y>>z;
      cs[i]=v3(x,y,z);
      cin>>rs[i];
    }
    cs.push_back(v3(1+huge_num,0.5,0.5));
    rs.push_back(huge_num);

    cs.push_back(v3(0.5,1+huge_num,0.5));
    rs.push_back(huge_num);

    cs.push_back(v3(0.5,0.5,1+huge_num));
    rs.push_back(huge_num);

    cs.push_back(v3(-huge_num,0.5,0.5));
    rs.push_back(huge_num);

    cs.push_back(v3(0.5,-huge_num,0.5));
    rs.push_back(huge_num);

    cs.push_back(v3(0.5,0.5,-huge_num));
    rs.push_back(huge_num);

    double ans=0;

    for (int i=0;i<50;i++){
      v3 cur((double)rand()/RAND_MAX,(double)rand()/RAND_MAX,(double)rand()/RAND_MAX);
      double dist=0.5;
      while (dist>1e-6){
        for (int i=0;i<50;i++){
          double worst=1e20;
          int wi;
          for (int i=0;i<cs.size();i++){
            double d=cs[i].dist(cur)-rs[i];
            if (worst>d){
              worst=d;
              wi=i;
            }
          }
          ans>?=worst;
          v3 ve(cur.x-cs[wi].x,cur.y-cs[wi].y,cur.z-cs[wi].z);
          double ab=ve.dist(v3(0,0,0));
          if (ab<1e-6){
            ve=v3((double)rand()/RAND_MAX-0.5,(double)rand()/RAND_MAX-0.5,(double)rand()/RAND_MAX-0.5);
            ab=ve.dist(v3(0,0,0));
          }
          ve.x*=dist/ab;
          ve.y*=dist/ab;
          ve.z*=dist/ab;
          cur.x+=ve.x;
          cur.y+=ve.y;
          cur.z+=ve.z;
        }
        dist/=2;
      }
    }
    cout<<ans<<endl;
  }
  return 0;
}