import java.math.BigDecimal;

import java.util.ArrayList;

import java.util.Collections;

import java.util.List;

import java.util.Scanner;

public class MathProblem

{

public static void main( String[] args )

{

Scanner s = new Scanner( System.in );

int t = s.nextInt();

while(t-->0)

{

int n = s.nextInt();

List<Segment> segments = new ArrayList<Segment>();

for(int i=0;i<n;i++)

{

Segment segment = new Segment();

segment.start = s.nextInt();

segment.end = s.nextInt();

segments.add( segment );

}

Collections.sort( segments, (o1,o2)->o1.start-o2.start );

int minEndTime = segments.get( 0 ).end;

int maxStartTime = segments.get( 0 ).start;

for(Segment seg : segments)

{

if(minEndTime>seg.end)

minEndTime= seg.end;

if(maxStartTime<seg.start)

maxStartTime = seg.start;

}

if(n>1)

System.out.println( (maxStartTime - minEndTime)>0?(maxStartTime - minEndTime):0);

else

System.out.println( 0 );

}

}

public static int barterMarket(int comicBooks, int coins, int coinsNeeded, int coinsOffered) {

BigDecimal comicBooksB = new BigDecimal(comicBooks);

BigDecimal coinsB = new BigDecimal(coins);

BigDecimal coinsNeededB = new BigDecimal(coinsNeeded);

BigDecimal coinsOfferedB = new BigDecimal(coinsOffered);

long num = comicBooksB.multiply( coinsOfferedB).add( coinsB).longValue();

long den = coinsOfferedB.add( coinsNeededB).longValue();

return (int)(num/den);

}

}

class Segment

{

int start;

int end;

}