def test_hidden(self):
        """test 'ls' behavior with hidden dotfiles."""
        # 1. test ignoring
        output = self.run_command("ls", exitcode=0)
        self.assertNotIn(".hidden", output)
        # 2. test -a
        output = self.run_command("ls -a", exitcode=0)
        self.assertIn(".hidden", output)
        self.assertIn(".", output)
        self.assertIn("..", output)
        self.assertIn("file1.txt", output)
        self.assertIn("file2.txt", output)
test 'ls' behavior with hidden dotfiles.
tests/ls/test_ls.py