import sys
input = sys.stdin.readline

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

    k = 0
    for i in range(N - 1):
        need = A[i] - A[i + 1] + 1
        if need > k:
            k = need

    if k < 0:
        k = 0

    print(k)