import java.io.*;
import java.util.*;
import java.util.function.*;
import java.util.stream.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int t = sc.nextInt();
        String result = IntStream.range(0, t).mapToObj(i -> {
            int n = sc.nextInt();
            int ans = 0;
            int prev = sc.nextInt();
            while (n-- > 1) {
                int x = sc.nextInt();
                if (x <= prev) {
                    ans = Math.max(ans, prev + 1 - x);
                }
                prev = x;
            }
            return String.valueOf(ans);
        }).collect(Collectors.joining("\n"));
        System.out.println(result);
    }
}
class Scanner {
    BufferedReader br;
    StringTokenizer st = new StringTokenizer("");
    StringBuilder sb = new StringBuilder();
    
    public Scanner() {
        try {
            br = new BufferedReader(new InputStreamReader(System.in));
        } catch (Exception e) {
            
        }
    }
    
    public int nextInt() {
        return Integer.parseInt(next());
    }
    
    public long nextLong() {
        return Long.parseLong(next());
    }
    
    public double nextDouble() {
        return Double.parseDouble(next());
    }
    
    public String next() {
        try {
            while (!st.hasMoreTokens()) {
                st = new StringTokenizer(br.readLine());
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            return st.nextToken();
        }
    }
    
}