T = int(input())

for _ in range(T):
	N = int(input())
	A = list(map(int,input().split()))
	ans = 0
	for i in range(len(A) - 1):
		a = A[i]
		b = A[i + 1]
		if b <= a:
			ans = max(ans,a - b + 1)
	print(ans)