# Enter your code here. Read input from STDIN. Print output to STDOUT
for _ in range(input()):
  dx = dict()
  dy = dict()
  count =0
  for _ in range(input()):
    x,y = map(int, raw_input().split())
    if x in dx.keys() or y in dy.keys():
      pass
    else:
      if x not in dx.keys():
        dx[x] = 1
      if y not in dy.keys():
        dy[y] = 1
      count += 1
  if count >1:
    print "NO"
  else:
    print "YES"