#include <cstdio>
#include <algorithm>
using namespace std;
int a[400];
int main() {
    int T,n,i,j,tot;  double ans;
    scanf("%d",&T);
    while (T--) {
        scanf("%d",&n); tot=0;
        for (i=1;i<=n;i++) scanf("%d",&a[i]);
        sort(a+1,a+n+1);
        for (i=1;i<=n;) {
            for (j=i;a[i]==a[j] && j<=n;j++) ;
            tot+=(j-i)*(i-1); i=j;
        }
        ans=(double)tot/(n*(n-1));
        printf("%.6lf\n",ans);
    }
}