# Enter your code here. Read input from STDIN. Print output to STDOUT
n = int(raw_input().strip())
for _ in xrange(n):
    q = int(raw_input().strip())
    pairs = [map(int, raw_input().strip().split(" ")) for p in xrange(q)]    
    is_true = True
    m_x = None
    m_y = None
    for p in pairs:        
        x,y = p
        if x!=0 and not m_x:
            m_x = [0, x]
        if y!=0 and not m_y:
           m_y = [0, y]        
        if m_x and x not in m_x:            
            print "NO"
            is_true = False            
            break
        if m_y and y not in m_y:            
            print "NO"
            is_true = False
            break
    if is_true:
        print "YES"