import sys
input = sys.stdin.readline

T=int(input())
for tests in range(T):
    N=int(input())
    A=list(map(int,input().split()))

    ANS=0

    for i in range(1,N):
        if A[i]-A[i-1]<=0:
            ANS=max(ANS,A[i-1]-A[i]+1)

    print(ANS)