from collections import *

t = int(input())

for _ in range(t):
    n = int(input())
    a = list(map(int, input().split()))
    d = defaultdict(int)
    for i in range(n):
        d[i] = a[i] # 初期座標
    ans = 0
    for i in range(n-1):
        if d[i] < d[i+1]:
            continue
        num = d[i] - d[i+1] + 1
        ans = max(ans,num)
    print(ans)