import sys
input = lambda :sys.stdin.readline()[:-1]
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
yes = lambda :print("yes");Yes = lambda :print("Yes")
no = lambda :print("no");No = lambda :print("No")
#######################################################################
for _ in range(ni()):
    n = ni()
    a = na()
    ans = 0
    for i in range(n-1):
        ans = max(ans,a[i]-a[i+1]+1)
    print(ans)