#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
void solve();
int main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int test_case;
  cin>>test_case;
  while (test_case--){
    solve();
  }
}
void solve(){
  int N;
  cin>>N;
  vector A(N,0);
  for(int &i:A)cin>>i;
  int ans=0;
  for(int i=0;i<N-1;i++){
    ans=max(ans,A[i]-A[i+1]+1);
  }
  cout<<ans<<'\n';
}