#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<algorithm>
#include<cmath>
#include<cstring>
#include<string>
#include<queue>
using namespace std;
const int imax=300+9;
int n,a[imax]; 

void iread()
{
    scanf("%d",&n);
    for(int i=1;i<=n;i++) scanf("%d",&a[i]); 
}

void iwork()
{
    double ans=0;
    for(int i=1;i<=n;i++)    
    {
        int cnt=0;
        for(int j=1;j<=n;j++) if(a[j]<a[i]) cnt++;
        ans+=(double)cnt/(double)n/(double)(n-1);    
    }
    printf("%.6lf\n",ans);
}

int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        iread();
        iwork();    
    }
    return 0;
}