# Enter your code here. Read input from STDIN. Print output to STDOUT
query=input()
for _ in range(query):
    l1=[]
    l2=[]
    n=input()

    for _ in range(n):
        raw = raw_input()
        
        l1.append(raw[0])
        l2.append(raw[2])
        
    len1=len(set(l1))
    len2=len(set(l2))
    if len1<=2 and len2<=2:
        print "YES"
    else:
        print "NO"