#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 1000000000000000001


int main(){
	
	int _t;
	cin>>_t;
	rep(_,_t){
		int n;
		cin>>n;
		vector<long long> x(n);
		long long ma = 0;
		rep(i,n){
			cin>>x[i];
			if(i>0)ma = max(ma,x[i-1]-x[i]+1);
		}
		cout<<ma<<endl;
	}
	
	return 0;
}