T=int(input())
for i in range(T):
  #D,A=map(int,input().split())
  N=int(input())
  X=list(map(int, input().split()))
  ans=0
  for i in range(N-1):
    p,q=X[i],X[i+1]
    if p>=q:
      c=p-q+1
      ans=max(ans,c)
  print(ans)