using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

            Program p = new Program();

​

        // Variables.

        int numTestCases = 0;

        int numPhoneNumbers = 0;

​

        // Save number of test cases.

        numTestCases = int.Parse(Console.ReadLine());

​

        // Do this for each test case.

        for (int i = 0; i < numTestCases; i++)

        {

            // Variables.

            var phoneNumbersList = new SortedSet<string>();

​

            bool pass = true;

​

            // Save number of phone numbers.

            numPhoneNumbers = int.Parse(Console.ReadLine());

​

            bool duplicate = false;

            HashSet<string> hashset = new HashSet<string>();

            string numberString;

            // Save all phonenumbers in the list.

            for (int j = 0; j < numPhoneNumbers; j++)

            {

                numberString = Console.ReadLine();

                if(!duplicate)

                {

                    if(hashset.Contains(numberString))

                    {

                        duplicate = true;

                    } else 

                    {

                        while(numberString.Length > 0 )

                        {

                            hashset.Add(numberString);

                            numberString = numberString.Remove(numberString.Length - 1);

                        }

                    }

                }

            }

            pass = !duplicate;

​

​

            // Write output.

            Console.WriteLine(pass ? "YES" : "NO");

            }

    }

    static bool isConsistent(string a,string b)

        {

            int len = a.Length;

​

            if (len > b.Length)

                return true;

​

            for (int i = 0; i < len; i++)

            {

                if (a[i] != b[i])

                    return true;

            }

​

            return false;

        }

}