using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static long[] NList => ReadLine().Split().Select(long.Parse).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var t = NN;
        var ans = new int[t];
        for (var u = 0; u < t; ++u)
        {
            var n = NN;
            var a = NList;
            var ok = 1_000_000_000;
            var ng = -1;
            while (ok - ng > 1)
            {
                var mid = (ok + ng) / 2;
                var flg = true;
                for (var i = 0L; i + 1 < n; ++i) if (a[i] + (i + 1) * mid >= a[i + 1] + (i + 2) * mid) flg = false;
                if (flg) ok = mid;
                else ng = mid;
            }
            ans[u] = ok;
        }
        WriteLine(string.Join("\n", ans));
    }
}