# Enter your code here. Read input from STDIN. Print output to STDOUT
require 'set'

q = gets.strip.to_i
q.times do
    n = gets.strip.to_i
    x = Set.new
    y = Set.new
    
    n.times do
        a, b = gets.strip.split.map(&:to_i)
        x << a
        y << b
    end
    
    puts x.size == 2 && y.size == 2 ? "YES" : "NO"
end