#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, s, e) for (int i = (int)(s); i < (int)(e); ++i)
#define all(a) (a).begin(),(a).end()

int main() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    
    int T;
    cin >> T;
    
    rep(testcase, 0, T) {
        int N;
        cin >> N;
        vector<ll> A(N);
        rep(i, 0, N) cin >> A[i];
        
        ll ans = 0;
        rep(i, 1, N) ans = max(ans, A[i - 1] - A[i] + 1);
        
        cout << ans << '\n';
    }
}