import sys
input=sys.stdin.readline
T=int(input().strip())
for _ in range(T):
    N=int(input().strip())
    A=list(map(int,input().split()))
    need=0
    for i in range(N-1):
        d=A[i]-A[i+1]+1
        if d>need: need=d
    print(max(0,need))