#define _USE_MATH_DEFINES
#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <queue>
#include <math.h>
#include <cmath>
#include <stack>
#include <map>
#include <set>
#include <numeric>
#include <iomanip>
#include <climits>
#include <functional>
#include <cassert>
#include <tuple>
using namespace std;
using ll = long long;

int T;

int main() {

    cin >> T;
    vector<ll> ans;
    while(T--) {
        int N;
        cin >> N;
        vector<ll> A(N+1);
        for(int i = 1; i <= N; ++i) cin >> A[i];

        ll l = -1, r = 1e10;
        while(r-l > 1) {
            ll mid = l+(r-l)/2;
            vector<ll> B(N+1);
            for(int i = 1; i <= N; ++i) B[i] = A[i]+mid*i;
            
            bool f = true;
            for(int i = 1; i <= N-1; ++i) {
                if(B[i+1] <= B[i]) {
                    f = false;
                    break;
                }
            }

            if(f) r = mid;
            else l = mid;
        }

        ans.push_back(r);
        
    }

    for(auto v : ans) cout << v << endl;

}