// #pragma GCC optimize("O3,unroll-loops")
#include <bits/stdc++.h>
// #include <x86intrin.h>
using namespace std;
#if __cplusplus >= 202002L
using namespace numbers;
#endif



int main(){
	cin.tie(0)->sync_with_stdio(0);
	cin.exceptions(ios::badbit | ios::failbit);
	auto __solve_tc = [&](auto __tc_num)->int{
		int n;
		cin >> n;
		vector<int> a(n);
		copy_n(istream_iterator<int>(cin), n, a.begin());
		int low = 0;
		for(auto i = 0; i < n - 1; ++ i){
			low = max(low, a[i] - a[i + 1] + 1);
		}
		cout << low << "\n";
		return 0;
	};
	int __tc_cnt;
	cin >> __tc_cnt;
	for(auto __tc_num = 0; __tc_num < __tc_cnt; ++ __tc_num){
		__solve_tc(__tc_num);
	}
	return 0;
}

/*
x+i*t < y + (i+1)*t

*/