# Enter your code here. Read input from STDIN. Print output to STDOUT
t=int(raw_input())
flag=False
for i in range(t):
    x_s=set()
    y_s=set()
    q=int(raw_input())
    for j in range(q):
        x,y=map(int,raw_input().split())
        len_x=len(x_s)
        len_y=len(y_s)
        x_s.add(x)
        y_s.add(y)
        if len(x_s)>2 or len(y_s)>2:
            if len_x!=len(x_s) and len_y!=len(y_s):
                flag=True
            else:
                continue
    if flag==True:
        print 'NO'
    else:
        print 'YES'