import sys
input = sys.stdin.readline
t=int(input())
for _ in range(t):
  n=int(input())
  a=list(map(int,input().split()))
  flg=True
  for i in range(n-1):
    if a[i]>=a[i+1]:
      flg=False
      break
  if flg:
    print(0)
    continue
  ok=10**9+10
  ng=0
  while ok-ng>1:
    mid=(ok+ng)//2
    flg=True
    for i in range(n-1):
      if a[i]+mid*(i+1)>=a[i+1]+mid*(i+2):
        flg=False
        break
    if flg:
      ok=mid
    else:
      ng=mid
  print(ok)