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

void solve(){
    int n;
    cin >> n;
    vector<long long> A(n);
    for (auto& a: A) cin >> a;

    long long l = 0;

    for (int i = 0; i < n-1; i++){
        long long a1 = A[i], a2 = A[i+1];
        
        if (a1 < a2) continue;

        long long dif = a1-a2 + 1;
        l = max(l,dif);

    }
    cout << l << endl;
}
int main() {
    int t;
    cin >> t;
    for (int i = 0; i < t; i++){
        solve();
    }
    return 0;
}