import collections,sys,math,functools,operator,itertools,bisect,heapq,decimal,string,time,random
#sys.setrecursionlimit(10**9)
#sys.set_int_max_str_digits(0)
input = sys.stdin.readline
t = int(input())
#alist = list(map(int,input().split()))
#alist = []
#s = input()
#n,m = map(int,input().split())
#for i in range(n):
#    alist.append(list(map(int,input().split())))
for i in range(t):
    n = int(input())
    a = list(map(int,input().split()))
    l,r = 0,10**10
    for j in range(42):
        m = (l+r)//2
        b = [a[k] + (k+1)*m for k in range(n)]
        cnt = 0
        for k in range(n-1):
            if b[k] < b[k+1]:
                cnt += 1
        if cnt == n-1:
            r = m
        else:
            l = m
    print(r)