def isok(x, a) -> bool:
    aa = []
    for i in range(len(a)):
        aa.append(a[i] + x * (i+1)) 
    
    for i in range(1, len(aa)):
        if aa[i-1] >= aa[i]:
            return False
    return True   

t = int(input())
for i in range(t):
    n = int(input())
    a = list(map(int, input().split()))
    
    ng = -1
    ok = 1 << 30
    for _ in range(30):
        md = (ng + ok) // 2
        if isok(md, a):
            ok = md
        else:
            ng = md
    print(ok)