T=input()
alpha="abcdefghijklmnopqrstuvwxyz";
for cs in xrange(T):
	n=input()
	ss=""
	for b in xrange(n):
		s=raw_input().strip()
		ss+=s[0]
	c=0
	for a in alpha:
		if(ss.count(a) > 1):
			print"NO"
			c=1
			break
	if c==0:
		print"YES"