content: import java.io.*;
  import java.math.*;
  import java.security.*;
  import java.text.*;
  import java.util.*;
  import java.util.concurrent.*;
  import java.util.regex.*;
  
  public class Solution {
  
    // Complete the gridChallenge function below.
    static String gridChallenge(String[] grid) {
      char[][] cache = new char[grid.length][grid[0].length()];
      for (int i = 0; i < grid.length; i++) {
        for (int j = 0; j < grid[i].length(); j++) {
          cache[i][j] = grid[i].charAt(j);
        }
        Arrays.sort(cache[i]);
  
        if (i != 0) {
          for (int j = 0; j < grid[i].length(); j++) {
            if (cache[i-1][j] > cache[i][j]) {
              return "NO";
            }
          }
        }
      }
  
      return "YES";
    }
  
    private static final Scanner scanner = new Scanner(System.in);
  
    public static void main(String[] args) throws IOException {
      BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH")));
  
      int t = scanner.nextInt();
      scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");
  
      for (int tItr = 0; tItr < t; tItr++) {
        int n = scanner.nextInt();
        scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");
  
        String[] grid = new String[n];
  
        for (int i = 0; i < n; i++) {
          String gridItem = scanner.nextLine();
          grid[i] = gridItem;
        }
  
        String result = gridChallenge(grid);
  
        bufferedWriter.write(result);
        bufferedWriter.newLine();
      }
  
      bufferedWriter.close();
  
      scanner.close();
    }
  }
  