package main

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

type FastScanner struct {
	r *bufio.Reader
}

func NewFastScanner() *FastScanner {
	return &FastScanner{r: bufio.NewReaderSize(os.Stdin, 1<<20)}
}

func (fs *FastScanner) NextInt64() int64 {
	var sign int64 = 1
	var val int64
	c, err := fs.r.ReadByte()
	for (c < '0' || c > '9') && c != '-' {
		c, err = fs.r.ReadByte()
		if err != nil {
			return 0
		}
	}
	if c == '-' {
		sign = -1
		c, _ = fs.r.ReadByte()
	}
	for c >= '0' && c <= '9' {
		val = val*10 + int64(c-'0')
		c, err = fs.r.ReadByte()
		if err != nil {
			break
		}
	}
	if err == nil {
		_ = fs.r.UnreadByte()
	}
	return val * sign
}

func max(a, b int64) int64 {
	if a > b {
		return a
	}
	return b
}

func min(a, b int64) int64 {
	if a < b {
		return a
	}
	return b
}

func feasible(k int64, l, r []int64) bool {
	L, R := int64(0), int64(0)
	for i := 0; i < len(l); i++ {
		nL := max(l[i], L-k)
		nR := min(r[i], R+k)
		if nL > nR {
			return false
		}
		L, R = nL, nR
	}
	return true
}

func main() {
	in := NewFastScanner()
	out := bufio.NewWriterSize(os.Stdout, 1<<20)
	defer out.Flush()

	t := int(in.NextInt64())
	for ; t > 0; t-- {
		n := int(in.NextInt64())
		l := make([]int64, n)
		r := make([]int64, n)
		for i := 0; i < n; i++ {
			l[i] = in.NextInt64()
			r[i] = in.NextInt64()
		}

		lo, hi := int64(-1), int64(1000000000)
		for hi-lo > 1 {
			mid := (lo + hi) / 2
			if feasible(mid, l, r) {
				hi = mid
			} else {
				lo = mid
			}
		}
		fmt.Fprintln(out, hi)
	}
}