import io
import sys
from collections import defaultdict, deque, Counter
from itertools import permutations, combinations, accumulate
from heapq import heappush, heappop
from bisect import bisect_right, bisect_left
from math import gcd
import math

_INPUT = """\
6
4
3
3 1 2
5
1 2 3 4 5
4
46 46 46 46
10
886822852 554802233 259460418 345136263 8466085 424914285 852474622 856826548 201867 777749594
"""

def input():
  return sys.stdin.readline()[:-1]

def solve(test):
  T=int(input())
  for _ in range(T):
    N=int(input())
    A=list(map(int, input().split()))
    ans=0
    for i in range(N-1):
      ans=max(ans,A[i]-A[i+1]+1)
    print(ans)

def random_input():
  from random import randint,shuffle
  N=randint(1,10)
  M=randint(1,N)
  A=list(range(1,M+1))+[randint(1,M) for _ in range(N-M)]
  shuffle(A)
  return (" ".join(map(str, [N,M]))+"\n"+" ".join(map(str, A))+"\n")*3

def simple_solve():
  return []

def main(test):
  if test==0:
    solve(0)
  elif test==1:
    sys.stdin = io.StringIO(_INPUT)
    case_no=int(input())
    for _ in range(case_no):
      solve(0)
  else:
    for i in range(1000):
      sys.stdin = io.StringIO(random_input())
      x=solve(1)
      y=simple_solve()
      if x!=y:
        print(i,x,y)
        print(*[line for line in sys.stdin],sep='')
        break

#0:提出用、1:与えられたテスト用、2:ストレステスト用
main(0)