<s>[INST] import random

def generate_password(n):
    """Generate a random password with fixed length n."""
    all_characters = string.ascii_letters + string.digits + string.punctuation
    if n < 8:
        print("Password length should be at least 8 characters.")
        return None
    password = ''.join(random.choice(all_characters) for _ in range(n))
    return password

import unittest
from unittest.mock import patch, MagicMock
from words_list import words

class TestPassword(unittest.TestCase):
    def setUp(self):
        self.password_length = 10
        self.words = words.words

    def test_function_description(self):
        with patch('random.choice', autospec=True) as mock_choice:
            mock_choice.return_value = 'c'
            password = generate_password(self.password_length)
            self.assertNotEquals(password, self.password_length*mock_choice.return_value)

    def test_length(self):
        # Use mocking to freeze a random value for accuracy
        with patch('random.choice', autospec=True) as mock_choice:
            mock_choice.return_value = 'c'
            password = generate_password(self.password_length)
            self.assertEqual(self.password_length, len(password))

    def test_mandatory_boxes_not_met(self):
        length = 5
        password = generate_password(length)
        self.assertIsNone(password)

if __name__ == '__main__':
    unittest.main()

Few things:
1. Ensure that `password` and `all_characters` are `bytes`, not string literals.
2. Even though optional, I've seen many places that use `.ascii_letters`, `.digits, `punctuation`, but did not stress the EXACT-SAME-SPECIFICATION details as in python documentation
3. The `patching strategy`: you are `@patching` only the interception on `random.choice`, what about in between failure probabilities?[/INST]