# Enter your code here. Read input from STDIN. Print output to STDOUT
n=int(input())
for i in range(n):
    m=int(input())
    x=set()
    y=set()
    
    for j in range(m):
        b=0
        d=0
        r=raw_input().split()
        if int(r[0]) in x:
            b+=1
        if int(r[1]) in y:
            d+=1
        x.add(int(r[0]))
        y.add(int(r[1]))
    if len(x)<=2+b or len(y)<=2+d:
        print "YES"
    else:
        print "NO"