package main

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

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

	var t int
	fmt.Fscan(reader, &t)
	for i := 0; i < t; i++ {
		var n int
		fmt.Fscan(reader, &n)
		maxL := -1
		minR := 2000000000
		for j := 0; j < n; j++ {
			var l, r int
			fmt.Fscan(reader, &l, &r)
			if l > maxL {
				maxL = l
			}
			if r < minR {
				minR = r
			}
		}
		ans := maxL - minR
		if ans < 0 {
			ans = 0
		}
		fmt.Fprintln(writer, ans)
	}
}