q = int(input().strip())

for i in range(q):
    t = int(input().strip())
    x,y = input().strip().split(' ')
    x,y = [int(x),int(y)]
    works = True
    for j in range(t - 1):
        x1,y1 = input().strip().split(' ')
        x1,y1 = [int(x1),int(y1)]
        if x1 != x and y1 != y:
            works = False
    if works:
        print('YES')
    else:
        print('NO')