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

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int T; cin >> T;
    while(T--){
        int N; cin >> N;
        vector<long long> A(N);
        for(auto &a : A) cin >> a;
        long long answer = 0;
        for(int i=0; i<N-1; i++) answer = max(answer,A.at(i)-A.at(i+1)+1);
        cout << answer << endl;
    }
}