#include <iostream>
#include <algorithm>
#include <vector>
#include <map>
#include <set>

using namespace std;

int main(){
  int n;
  cin>>n;
  int m;
  while (n--){
    cin>>m;
    int nums[m];
    for (int i=0; i<m; ++i){
      scanf("%d", &nums[i]);
    }
    int sum=m*(m-1);
    sort(nums, nums+m);
    int ok=0;
    for (int i=0; i<m-1; ++i){
      for (int j=i+1; j<m; ++j){
        if (nums[i]<nums[j])  ++ok;
      }
    }
    double result=(double)ok/sum;
    printf("%.6lf\n", result);
  }
  return 0;
}