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#include<algorithm>
#include<utility>
#include<cmath>
#define N 500
using namespace std;
typedef pair<int, int> Coord;
struct
{
int a, b;
double dis;
bool operator<(const Edge& e){ return dis < e.dis; }
}edge[126000];
int p[N];
inline void init(int n);
inline int find(int a);
inline void Union(int a, int b);
inline double getDistance(Coord& a, Coord& b);
double kruskal(int V, int E, int S);
int main()
{
Coord coord[N];
int Case;
scanf("%d", &Case);
while (Case--)
{
int S, P, i;
scanf("%d%d", &S, &P);
for (i = 0; i < P; i++)
scanf("%d%d", &coord[i].first, &coord[i].second);
int e = 0;
for (i = 0; i < P; i++)
for (int j = i + 1; j < P; j++)
{
edge[e].a = i;
edge[e].b = j;
edge[e++].dis = getDistance(coord[i], coord[j]);
}
printf("%.2lfn", kruskal(P, e, S));
}
return 0;
}
double getDistance(Coord& a, Coord& b)
{
return sqrt((a.first - b.first)*(a.first - b.first) + (a.second - b.second)*(a.second - b.second));
}
void init(int n)
{
for (int i = 0; i < n; i++)
p[i] = i;
}
int find(int a)
{
return a == p[a] ? a : (p[a] = find(p[a]));
}
void Union(int a, int b)
{
p[find(a)] = find(b);
}
double kruskal(int V, int E, int S)
{
init(V);
sort(edge, edge + E);
double D = 0;
for (int i = 1, e = 0; i < V - (S - 1) && e < E; i++)
{
while (find(edge[e].a) == find(edge[e].b))
e++;
Union(edge[e].a, edge[e].b);
D = edge[e].dis;
e++;
}
return D;
}
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