#include<iostream>
#include<vector>
#include<bitset>
#include<algorithm>
#include<cmath>
#include<string>
#include<queue>
#include<numeric>//iota -- iota(all(a), x) a从头到尾从x开始递增
#include<cstring>
#include<ctime>
#include<array>
#include<list>
#include<random>
#include<tuple>
#include<deque>
#include<map>
#include<stack>
#include<set>
using namespace std;
#define IOS ios::sync_with_stdio(false);cin.tie(0), cout.tie(0)
#define int long long
#define all(x) x.begin(), x.end()
#define pb push_back
#define pf push_front
#define lowbit(x) (x & (-x))
const int xy[][2] = { 0,1, 0, -1, 1, 0, -1, 0 };
#define mem(a, x) memset(a, x, sizeof a)
typedef long long ll;
typedef pair<int, int> PII;
typedef pair<double, double> PDD;
typedef pair<char, char> PCC;
typedef pair<int, char> PIC;
typedef pair<char, int> PCI;
#define x first
#define y second
#define NO cout << "NO\n"
#define YES cout << "YES\n"
inline int read();
const int INF = 1e9, N = 1e4 + 10, MOD = 998244353, M = 1e4 + 10, K = 131;
const double PI = acos(-1.0);
void solve() {
    int n; cin >> n;
    vector<int>a(n + 2), pre(n + 2, 0);
    for (int i = 1; i <= n; i++)cin >> a[i], pre[i] = pre[i - 1] + a[i];
    int u = 0;
    for(int i = 2; i < n; i++)
        if (a[i] < a[i - 1] && a[i] < a[i + 1]) {
            u = i;
            break;
        }
    int l = 1, r = n;
    while (r - l + 1 > 3) {
        while (a[r] < r - l + 1 && r > u + 1)r--;
        while (a[l] < r - l + 1 && l < u - 1)l++;
        if ((a[r] >= r - l + 1 && a[l] >= r - l + 1) || r - l + 1 == 3)break;
    }
    printf("%.11lf\n", 1.0 * (pre[r] - pre[l - 1]) / (r - l + 1));
}
signed main() {
    IOS;
    int _ = 1;
    cin >> _;
    while (_--)solve();
    return 0;
}
inline int read()
{
    int x = 0, f = 1; char ch = getchar();
    while (ch < '0' || ch>'9') { if (ch == '-') f = -1; ch = getchar(); }
    while (ch >= '0' && ch <= '9') { x = x * 10 + ch - 48; ch = getchar(); }
    return x * f;
}
/*   /\_/\
*   (= ._.)
*   / >  \>
*/