T=int(input())
for _ in range(T):
    N=int(input())
    A=list(map(int,input().split()))
    ng=-1
    ok=int(1e18)
    
    def f(x):
        B=[A[0]+x]
        for i in range(1,N):
            b=A[i]+(i+1)*x
            if B[-1]>=b:return False
            B.append(b)
        return True

    while ok-ng>1:
        m=(ok+ng)//2
        if f(m):ok=m
        else:ng=m
    print(ok)