import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;

public class Main {
	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		int t = Integer.parseInt(br.readLine());
		PrintWriter pw = new PrintWriter(System.out);
		for (int z = 0; z < t; z++) {
			int n = Integer.parseInt(br.readLine());
			String[] sa = br.readLine().split(" ");
			int[] a = new int[n];
			for (int i = 0; i < n; i++) {
				a[i] = Integer.parseInt(sa[i]);
			}

			int max = -1;
			for (int i = 1; i < n; i++) {
				max = Math.max(max, a[i - 1] - a[i]);
			}
			pw.println(max + 1);
		}
		pw.flush();
		br.close();
	}
}