#include <cstdio>
#include <memory.h>
#include <cstdlib>
#include <algorithm>
#include <iostream>
#include <utility>
#include <vector>
#include <set>
#include <map>
#include <cmath>
#include <string>
#include <ctime>

using namespace std;

#define forn( i,n ) for ( int i=0; i<(int)(n); i++ )
#define pb push_back
#define mp make_pair
#define sz(a) (int)((a).size())
typedef long long ll;
typedef double ld;
typedef pair<int,int> pii;
typedef pair<double,int> pdi;

const int maxn = 2010;
const ld PI = acos( -1.0 );

int n, L, x1[maxn], _y1[maxn], x2[maxn], y2[maxn];
pdi ev[maxn*2];
int ke;

bool getSeg( ld x1, ld _y1, ld x2, ld y2, ld& res ) {
  if ( _y1*y2 > 1e-7 ) return false;
  res = x1 + ( x2-x1 )*fabs( _y1 )/( fabs( _y1 ) + fabs( y2 ) );
  return true;
}

bool getCircle( ld xx, ld yy, ld rr, ld& ci, ld& ca ) {
  if ( fabs( yy ) > rr ) return false;
  ld dx = sqrt( rr*rr - yy*yy );
  ci = xx - dx;
  ca = xx + dx;
  return true;
}

ld min( ld a, ld b ) {
  return a < b ? a : b;
}

ld max( ld a, ld b ) {
  return a > b ? a : b;
}

bool check( double R ) {
  ke = 0;
  forn( i, n ) {
    ld mi = 1e9;
    ld ma = -1e9;
    ld ci, ca;
    if ( getCircle( x1[i], _y1[i], R, ci, ca ) ) {
      mi = min( mi, ci );
      ma = max( ma, ca );
    }

    if ( getCircle( x2[i], y2[i], R, ci, ca ) ) {
      mi = min( mi, ci );
      ma = max( ma, ca );
    }

    ld an = atan2( y2[i]-_y1[i], x2[i]-x1[i] ) - PI/2;
    ld dx = R * cos( an );
    ld dy = R * sin( an );
    if ( _y1[i] > y2[i] ) {
      if ( getSeg( x1[i]+dx, _y1[i]+dy,
                   x2[i]+dx, y2[i]+dy, ci ) ) mi = min( mi, ci );
      if ( getSeg( x1[i]-dx, _y1[i]-dy,
                   x2[i]-dx, y2[i]-dy, ca ) ) ma = max( ma, ca );
    }
    else
    {
      if ( getSeg( x1[i]+dx, _y1[i]+dy,
                   x2[i]+dx, y2[i]+dy, ca ) ) ma = max( ma, ca );
      if ( getSeg( x1[i]-dx, _y1[i]-dy,
                   x2[i]-dx, y2[i]-dy, ci ) ) mi = min( mi, ci );
    }

    if ( mi < 1e8 ) {
      ev[ke++] = pdi( max( mi, 0.0 ), -1 );
      ev[ke++] = pdi( min( ma, 1.0*L ), +1 );
    }
  }

  sort( ev, ev+ke );

  int bal = 0;
  if ( ke == 0 || ev[0].first > 1e-7 ) return true;
  forn( i, ke ) {
    bal += ev[i].second;
    if ( bal == 0 && ( i < ke-1 || ev[i].first < L-1e-7 ) ) return true;
  }

  return false;
}

int main()
{
  freopen( "c.in", "r", stdin );

  int tc;
  scanf( "%d", &tc );
  while ( tc-- ) {
    scanf( "%d %d", &n, &L );
    forn( i, n ) {
      scanf( "%d %d %d %d", &x1[i], &_y1[i], &x2[i], &y2[i] );
      if ( x1[i] > x2[i] ) {
        swap( x1[i], x2[i] );
        swap( _y1[i], y2[i] );
      }
    }

    double l = 0, r = L, m;
    forn( it, 500 ) {
      m = ( l+r ) * 0.5;
      if ( check( m ) ) l = m;
      else r = m;
    }

    printf( "%.3f\n", l );
  }

  return 0;
}