#include <iostream>

int T, n, t[100001];

int main() {
    std::cin >> T;
    while (T--) {
        std::cin >> n;
        for (int i = 1; i <= n; i++) {
            std::cin >> t[i];
        }
        int answer = 0;
        for (int i = 1; i <= n; i++) {
            for (int j = 1; j <= n; j++)
                if (t[i] > t[j]) answer++;
        }
        printf("%.6f\n", 1.0 * answer / n / (n - 1));
    }
    return 0;
}