package main

import . "fmt"
import . "os"
import bf "bufio"

func main() {
	rd:=bf.NewReader(Stdin)
	var t int
	Fscan(rd,&t)
	a := make([]int, 2e5)
	for ;t>0;t-- {
		var n int
		Fscan(rd,&n)
		a = a[:n]
		for i := range a {
			Fscan(rd,&a[i])
		}
		ans := 0
		for i, v := range a[1:] {
			ans = max(ans, a[i]-v+1)
		}
		Println(ans)
	}
}