#include<bits/stdc++.h>

using namespace std;
using ll=long long;

int main(){
    int T; cin >> T;

    for (int t = 1; t <= T; t++){
        int N; cin >> N;
        vector<int> A(N+1);
        for (int i = 1; i <=N; i++) cin >> A[i];

        int K = 0;
        for (int i = 1; i <= N-1; i++) K = max(K, A[i]-A[i+1]+1);
        cout << K << "\n";
    }
    return 0;
}