t=int(raw_input())
for i in xrange(t):
    q=int(raw_input())
    p=[]
    for j in xrange(q):
        p.append(map(int, raw_input().split()))  
    p.sort()    
    t=1
    for j in xrange(1,len(p)-1):
        if(not (p[j][0] == p[j-1][0] or p[j][1]==p[j-1][1])  and 
           not (p[j][0] == p[j+1][0] or p[j][1]==p[j+1][1])):
            t=0
            break
    if(t==0):
        print "NO"
    else:
        print "YES"