import java.util.*;
import java.io.*;
public class Main {
public static void main(String[] args) throws IOException {
BufferedReader br= new BufferedReader(new InputStreamReader(System.in));
int n = Integer.parseInt(br.readLine());
for(int i=0;i<n;i++) {
int t = Integer.parseInt(br.readLine());
String [] arr= new String[t];
int sw=0;
for(int j=0;j<t;j++) {
arr[j]=br.readLine();
}
Arrays.sort(arr, new Comparator<String>() {
@Override
public int compare(String o1, String o2) {
return o1.compareTo(o2);
}
});
for(int j=1;j<t;j++) {
if(arr[j].startsWith(arr[j-1])) {
sw=1;
break;
}
}
System.out.println(sw==0?"YES":"NO");
}
}
}