for _ in range(int(input())):
    N = int(input())
    A = list(map(int, input().split()))
    ans = 0
    for i in range(N - 1):
        if A[i] < A[i + 1]:
            continue
        else:
            ans = max(ans, A[i] - A[i + 1] + 1)
    print(ans)