T=int(input())
assert 1<=T<=10**5
Nsum=0
for i in range(T):
	N=int(input())
	Nsum+=N
	assert Nsum<=2*10**5
	assert 2<=N<=2*10**5
	A=list(map(int,input().split()))
	ans=0
	for i in range(N-1):
		assert 0<=A[i]<=10**9
		assert 0<=A[i+1]<=10**9
		ans=max(ans,A[i]-A[i+1]+1)
	print(ans)
#input()