#include <bits/stdc++.h>
#define ll long long
#define inf 0x3f3f3f3f
#define eps 1e-9
#define rep(i,a,b) for(int i=(a);i<=(b);i++)
#define dep(i,a,b) for(int i=(a);i>=(b);i--)
#define lowbit(a) (a)&(-a)
using namespace std;
const int maxn = 125005; // P<=500，最大边数约为125000，统一采用maxn开辟
const int mo = 998244353;
const double pi = acos(-1.0);
template <typename T>
inline void read(T &X)
{
    X = 0;int w = 0; char ch = 0;
    while(!isdigit(ch)) {w |= ch == '-' ;ch = getchar();}
    while(isdigit(ch)) X = X * 10 + (ch^48),ch = getchar();
    if(w) X = -X;
}
int s,p;
int x[maxn],y[maxn];
struct Edge
{
    int u,v;
    double w;
}e[maxn];
bool cmp(Edge A,Edge B)
{
    return A.w < B.w;
}
int fa[maxn];
int find(int u)
{
    if(u == fa[u]) return u;
    return fa[u] = find(fa[u]);
}
void solve()
{
    read(s),read(p);
    rep(i,1,p) read(x[i]),read(y[i]);
    if(s >= p)
    {
        cout << fixed << setprecision(2) << 0.00 << endl;
        return;
    }
    int m = 0;
    rep(i,1,p)
    {
        rep(j,i+1,p)
        {
            m++;
            e[m].u = i;
            e[m].v = j;
            e[m].w = sqrt((double)(x[i]-x[j])*(x[i]-x[j]) + (double)(y[i]-y[j])*(y[i]-y[j]));
        }
    }
    rep(i,1,p) fa[i] = i;
    sort(e+1,e+1+m,cmp);
    int cnt = 0;
    double ans = 0;
    rep(i,1,m)
    {
        int fu = find(e[i].u);
        int fv = find(e[i].v);
        if(fu != fv)
        {
            fa[fu] = fv;
            ans = e[i].w; 
            cnt++;
        }
        if(cnt == p-s) break;
    }
    cout << fixed << setprecision(2) << ans << endl;
    return;
}
int main()
{
    int T=1;
//  freopen("mul.in","r",stdin);
//  freopen("mul.out","w",stdout);
    read(T); // 此题为多组测试数据，直接解除注释即可完美运行！
    while(T--) solve();
    return 0;
}