# Enter your code here. Read input from STDIN. Print output to STDOUT
q=int(raw_input())

for i in range(q):
    n=int(raw_input())
    YES=True
    x_list=[]
    y_list=[]
    for j in range(n):
        
        x,y=map(int,raw_input().split())

        if len(x_list) < 2 and (x not in x_list):
            x_list.append(x)

        if len(y_list) < 2 and (y not in y_list):
            y_list.append(y)

        if len(x_list)==2 and len(y_list)==2 and (x not in x_list) and (y not in y_list):    
            YES=False
        #print(x_list)
        #print(y_list)
    if YES:
        print("YES")
    else:
        print("NO")