for t in range(int(input())):
d= dict()
n = int(input())
L = []
for i in range(n):
s = input()
L.append(s)
k = ""
for i in range(len(s)):
k+=s[i]
try:
d[k] +=1
except:
d[k] = 1
for i in L:
if d[i] > 1:
print("NO")
break
else:
print("YES")