package main

import (
	"bufio"
	"fmt"
	"os"
)

func main() {
	in := bufio.NewReader(os.Stdin)
	out := bufio.NewWriter(os.Stdout)
	defer out.Flush()

	var t int
	fmt.Fscan(in, &t)
	for i := 0; i < t; i++ {
		var n int64
		fmt.Fscan(in, &n)
		var mx, sum int64
		for j := int64(0); j < n; j++ {
			var a int64
			fmt.Fscan(in, &a)
			if a > mx {
				mx = a
			}
			sum += a
		}
		k := mx
		k2 := (sum + n - 2) / (n - 1)
		if k2 > k {
			k = k2
		}
		fmt.Fprintln(out, k*(n-1)-sum)
	}
}