#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int N;
int A[201010];
void solve(){
    cin >> N;
    for(int i = 0;i < N;i++)cin >> A[i];
    int mx = 0;
    for(int i = 0;i < N - 1;i++){
        mx = max(mx, A[i] - A[i + 1] + 1);
    }
    cout << mx << "\n";
}
int main(void){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    
    int t; cin >> t;
    while(t--)solve();
    return 0;
}