q = int(input())

def check(b, max1):
    output = "YES"
    for coord in b:
        if ((coord[0] == 0) and (coord[1] <= max1)):
            continue
        elif ((coord[0] <= max1) and (coord[1] == 0)):
            continue
        elif ((coord[0] == max1) and (coord[1] == max1)):
            continue
        else:
            output = "NO"
            return output
    return output   

for i in range(q):
    y = int(input())
    max1 = 0
    b = []
    for j in range(y):
        a = a = input().split()
        a = list(map(int, a))
        if max(a)> max1:
            max1 = max(a)
        b.append(a)
    #print(max1)
    print(check(b, max1))