q = int(input())

for i in range(q):
    n = int(input())
    
    xedges = []
    yedges = []
    isRect = True
    
    for j in range(n):
        xy = input().split()
        x = int(xy[0])
        y = int(xy[1])
        
        if len(xedges) < 2:
            xedges.append(x)
            yedges.append(y)
        else:
            if x not in xedges and y not in yedges:
                print("NO")
                isRect = False
                break
    if isRect:            
        print("YES")