#include <bits/stdc++.h>
using namespace std;
const long long MAX = 500005;
const double INF = 1e9;
long long t, n, k, l, r;
long long a[MAX], q1[MAX], q2[MAX], q[MAX];
double val[MAX];
double ans;
//读入优化
double read() {double ret = 0, f = 1;char ch = getchar();while ('0' > ch || ch > '9') {if (ch == '-') f = -1;ch = getchar();}while ('0' <= ch && ch <= '9') {ret = ret * 10 + ch - '0';ch = getchar();}return ret * f;
}
//判断
bool judge(double m) {double ret = -INF;for (long long i = 1; i <= n; i++) {val[i] = a[i] - m * i;}long long head = 1, tail = 0;for (long long i = l + 1; i <= n; i++) {while (head <= tail && i - q[head] >= r) head++;while (head <= tail && val[q[tail]] >= val[i - l]) tail--;q[++tail] = i - l;ret = max(ret, val[i] - val[q[head]]);}for (long long i = 1; i <= n; i++) {val[i] = a[i] + m * i;}head = 1, tail = 0;for (long long i = n - l; i >= 1; i--) {while (head <= tail && q[head] - i >= r) head++;while (head <= tail && val[q[tail]] >= val[i + l]) tail--;q[++tail] = i + l;ret = max(ret, val[i] - val[q[head]]);}//k是题目给的常数 return ret >= k * m;
}
int main() {t = read();while (t--) {ans = -INF;n = read(), k = read(), l = read(), r = read();for (long long i = 1; i <= n; i++) a[i] = read();long long h1 = 1, h2 = 1, t1 = 0, t2 = 0;for (long long i = 1; i < l; i++) {while (h1 <= t1 && a[q1[t1]] >= a[i]) t1--;while (h2 <= t2 && a[q2[t2]] <= a[i]) t2--;q1[++t1] = q2[++t2] = i; }for (long long i = 1; i <= n; i++) {while (h1 <= t1 && i - q1[h1] >= l) h1++;while (h2 <= t2 && i - q2[h2] >= l) h2++;while (h1 <= t1 && a[q1[t1]] >= a[i]) t1--;while (h2 <= t2 && a[q2[t2]] <= a[i]) t2--;q1[++t1] = q2[++t2] = i;ans = max(ans, 1.0 * (a[q2[h2]] - a[q1[h1]]) / (l + k - 1));}//注意精度 double l = 0, r = 1000;while (r - l >= 0.000001) {double mid = (l + r) / 2;if (judge(mid)) ans = max(ans, mid), l = mid + 0.000001;else r = mid - 0.000001;}printf("%.4lf\n", ans);}return 0;
}