#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);
        for(int i = 0; i < N; ++i) cin >> A[i];
        ll mx = 0;
        for(int i = 0; i < N-1; ++i) {
            mx = max(mx, A[i]-A[i+1]+1);
        }

        ans.push_back(mx);
    }

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

}