string gridChallenge(vector<string> grid) {
    for(int i = 0; i < grid.size(); i++) sort(grid[i].begin(), grid[i].end());
    for(int col = 0; col < grid.size(); col++){
       for(int row = 1; row < grid.size(); row++)
            if(grid[row][col] < grid[row-1][col]) return "NO";
    }
    return "YES";
}

def gridChallenge(grid):
    grid = [sorted(list(row)) for row in grid]
    for col in range(len(grid[0])):
        for row in range(1, len(grid)):
            if grid[row][col] < grid[row - 1][col]:
                return "NO"
    return "YES"

def gridChallenge(grid):
    # Write your code here
    for i in range(0,len(grid)):
        grid[i]=''.join(sorted(grid[i]))
    
    for col in range(0,len(grid[0])):
        anch=-999
        for row in range(0,len(grid)):
            if anch> ord(grid[row][col]) :
                return "NO"
            anch=ord(grid[row][col])
    
    return "YES"

module Main where

import Control.Monad (replicateM, replicateM_)
import Data.List (sort, transpose)

solve :: (Ord a) => [[a]] -> Bool
solve grid = all (\xs -> xs == sort xs) $ transpose $ map sort grid

main :: IO ()
main = do
    cases <- readLn :: IO Int
    replicateM_
        cases
        ( do
            n <- readLn :: IO Int
            grid <- replicateM n getLine
            putStrLn $ if solve grid then "YES" else "NO"
        )