def solve():
    N = int(input())
    A = list(map(int, input().split()))

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

    return K

#==================================================
import sys
input=sys.stdin.readline
write=sys.stdout.write

T = int(input())
write("\n".join(map(str, [solve() for _ in range(T)])))